Cambridge IGCSE · thinka-original Practice Paper

2023 Cambridge IGCSE Mathematics (0580) Practice Paper with Answers

Thinka Nov 2023 (V2) Cambridge IGCSE-Style Mock — Mathematics (0580)

200 marks240 mins2023
An original Thinka practice paper modelled on the structure and difficulty of the Nov 2023 (V2) Cambridge IGCSE Mathematics (0580) paper. Not affiliated with or reproduced from Cambridge.

Paper 22 Extended

Answer all questions. Use a calculator where appropriate. Show all necessary working clearly.
26 Question · 75 marks
Question 1 · short_answer
2 marks
A company's profits increased by 12% in 2021 and then decreased by 8% in 2022.

Calculate the overall percentage increase in the profits from the start of 2021 to the end of 2022.
Show answer & marking scheme

Worked solution

Let the initial profits be \(P\).

At the end of 2021, the profits are \(1.12P\).
At the end of 2022, the profits are:
\(1.12P \times (1 - 0.08) = 1.12P \times 0.92 = 1.0304P\).

The overall percentage increase is:
\((1.0304 - 1) \times 100 = 3.04\%\).

Marking scheme

M1 for \(1.12 \times 0.92\) or \(1.0304\) seen
A1 for 3.04
Question 2 · short_answer
3 marks
A solid metal cylinder has a radius of 4 cm and a height of 10 cm.
It is melted down and recast into a solid sphere.

Calculate the radius of the sphere.
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Worked solution

The volume of a cylinder is given by:
\(V_{\text{cylinder}} = \pi r^2 h = \pi \times 4^2 \times 10 = 160\pi\text{ cm}^3\).

The volume of a sphere is given by:
\(V_{\text{sphere}} = \frac{4}{3}\pi R^3\).

Equating the two volumes:
\(\frac{4}{3}\pi R^3 = 160\pi\)
\(\frac{4}{3}R^3 = 160\)
\(R^3 = 120\)
\(R = \sqrt[3]{120} \approx 4.93\text{ cm}\) (correct to 3 significant figures).

Marking scheme

M1 for volume of cylinder expression \(\pi \times 4^2 \times 10\) or \(160\pi\) (or 502.7...)
M1 for equating to volume of sphere formula \(\frac{4}{3}\pi R^3 = \text{their Volume}\)
A1 for 4.93 (accept 4.932...)
Question 3 · short_answer
3 marks
Rearrange the formula to make \(x\) the subject:

\(y = \frac{5 - 2x}{3x + 4}\)
Show answer & marking scheme

Worked solution

Multiply both sides by \(3x + 4\):
\(y(3x + 4) = 5 - 2x\)
\(3xy + 4y = 5 - 2x\)

Collect the terms in \(x\) on one side of the equation:
\(3xy + 2x = 5 - 4y\)

Factorise \(x\):
\(x(3y + 2) = 5 - 4y\)

Divide by \(3y + 2\):
\(x = \frac{5 - 4y}{3y + 2}\)

Marking scheme

M1 for multiplying by denominator to clear fraction: \(y(3x + 4) = 5 - 2x\)
M1 for collecting \(x\) terms on one side and factorising: \(x(3y + 2) = 5 - 4y\)
A1 for \(x = \frac{5 - 4y}{3y + 2}\) (or equivalent)
Question 4 · short_answer
3 marks
A bag contains 5 red balls, 3 blue balls, and 2 green balls.
Two balls are selected at random from the bag without replacement.

Calculate the probability that both balls are of the same colour.
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Worked solution

The total number of balls is \(5 + 3 + 2 = 10\).

Since selection is without replacement:
\(\text{P(both Red)} = \frac{5}{10} \times \frac{4}{9} = \frac{20}{90}\)
\(\text{P(both Blue)} = \frac{3}{10} \times \frac{2}{9} = \frac{6}{90}\)
\(\text{P(both Green)} = \frac{2}{10} \times \frac{1}{9} = \frac{2}{90}\)

Total probability of the same colour is:
\(\frac{20}{90} + \frac{6}{90} + \frac{2}{90} = \frac{28}{90} = \frac{14}{45}\) (or approximately \(0.311\)).

Marking scheme

M1 for at least one correct product of probabilities without replacement (e.g. \(\frac{5}{10} \times \frac{4}{9}\))
M1 for adding three correct products: \(\frac{5}{10} \times \frac{4}{9} + \frac{3}{10} \times \frac{2}{9} + \frac{2}{10} \times \frac{1}{9}\)
A1 for \(\frac{14}{45}\) or 0.311 (accept 0.311 or 0.3111...)
Question 5 · short_answer
2 marks
A ladder of length 6.5 m leans against a vertical wall. The foot of the ladder is 2.5 m away from the base of the wall on horizontal ground.

Calculate the angle that the ladder makes with the ground.
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Worked solution

In the right-angled triangle formed, the ladder is the hypotenuse (6.5 m) and the distance along the ground is the adjacent side (2.5 m).

\(\cos(\theta) = \frac{\text{Adjacent}}{\text{Hypotenuse}} = \frac{2.5}{6.5}\)
\(\theta = \cos^{-1}\left(\frac{2.5}{6.5}\right) \approx 67.4^\circ\) (correct to 1 decimal place).

Marking scheme

M1 for \(\text{cos}(\theta) = \frac{2.5}{6.5}\) or equivalent correct trig statement
A1 for 67.4 (accept 67.38...)
Question 6 · short_answer
3 marks
The table below shows the frequency of the number of goals scored by a football team in 40 matches.

| Goals Scored | Frequency |
|---|---|
| 0 | 8 |
| 1 | 15 |
| 2 | 11 |
| 3 | 4 |
| 4 | 2 |

Calculate the mean number of goals scored per match.
Show answer & marking scheme

Worked solution

Find the total goals scored:
\(0 \times 8 + 1 \times 15 + 2 \times 11 + 3 \times 4 + 4 \times 2 = 0 + 15 + 22 + 12 + 8 = 57\text{ goals}\).

The total number of matches is 40.

\(\text{Mean} = \frac{57}{40} = 1.425\text{ goals per match}\).

Marking scheme

M1 for showing sum of products (at least 3 correct products shown added, e.g. \(15 + 22 + 12 + 8\))
M1 for dividing their sum by 40
A1 for 1.425
Question 7 · short_answer
3 marks
In triangle \(ABC\), \(AB = 7\text{ cm}\), \(BC = 9\text{ cm}\), and angle \(ABC = 62^\circ\).

Calculate the length of \(AC\).
Show answer & marking scheme

Worked solution

Using the Cosine Rule:
\(AC^2 = AB^2 + BC^2 - 2(AB)(BC)\cos(ABC)\)
\(AC^2 = 7^2 + 9^2 - 2(7)(9)\cos(62^\circ)\)
\(AC^2 = 49 + 81 - 126\cos(62^\circ)\)
\(AC^2 = 130 - 126(0.46947) = 130 - 59.153 = 70.847\)

\(AC = \sqrt{70.847} \approx 8.42\text{ cm}\) (correct to 3 significant figures).

Marking scheme

M1 for correct substitution into the Cosine Rule: \(7^2 + 9^2 - 2 \times 7 \times 9 \times \cos(62^\circ)\)
M1 for \(AC^2 \approx 70.8\) or better
A1 for 8.42 (accept 8.417...)
Question 8 · short_answer
3 marks
Find the positive \(x\)-coordinate of the stationary point on the curve:

\(y = 2x^3 - 9x^2 - 24x + 5\)
Show answer & marking scheme

Worked solution

Differentiate the function with respect to \(x\):
\(\frac{dy}{dx} = 6x^2 - 18x - 24\)

At a stationary point, the gradient \(\frac{dy}{dx} = 0\):
\(6x^2 - 18x - 24 = 0\)

Divide by 6:
\(x^2 - 3x - 4 = 0\)

Factorise the quadratic:
\((x - 4)(x + 1) = 0\)

This gives \(x = 4\) or \(x = -1\).
Since we require the positive \(x\)-coordinate, \(x = 4\).

Marking scheme

M1 for correct differentiation of at least two terms of the cubic expression
M1 for setting their derivative to 0 and solving the resulting quadratic equation
A1 for 4
Question 9 · short_answer
3 marks
A rectangular field has a length of $80\text{ m}$, correct to the nearest metre, and a width of $45\text{ m}$, correct to the nearest $5\text{ m}$.

Calculate the upper bound for the perimeter of the field.
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Worked solution

To find the upper bound for the perimeter, we first determine the upper bounds for both the length and the width.

For the length, $L = 80\text{ m}$ to the nearest metre, so its upper bound is:
$$L_{\text{upper}} = 80 + 0.5 = 80.5\text{ m}$$

For the width, $W = 45\text{ m}$ to the nearest $5\text{ m}$, so its upper bound is:
$$W_{\text{upper}} = 45 + 2.5 = 47.5\text{ m}$$

The perimeter $P$ is given by:
$$P = 2(L + W)$$

Therefore, the upper bound of the perimeter is:
$$P_{\text{upper}} = 2(L_{\text{upper}} + W_{\text{upper}}) = 2(80.5 + 47.5) = 2(128) = 256\text{ m}$$

Marking scheme

M1 for $L_{\text{upper}} = 80.5$ or $W_{\text{upper}} = 47.5$ seen
M1 for $2(\text{their } L_{\text{upper}} + \text{their } W_{\text{upper}})$
A1 for 256
Question 10 · short_answer
3 marks
Rearrange the formula to make $t$ the subject.
$$w = \frac{3t - 5}{t + 2}$$
Show answer & marking scheme

Worked solution

Multiply both sides by $t + 2$:
$$w(t + 2) = 3t - 5$$

Expand the bracket:
$$wt + 2w = 3t - 5$$

Rearrange the terms to group all terms with $t$ on one side:
$$2w + 5 = 3t - wt$$

Factorise $t$ on the right-hand side:
$$2w + 5 = t(3 - w)$$

Divide both sides by $3 - w$:
$$t = \frac{2w + 5}{3 - w}$$

Marking scheme

M1 for $w(t + 2) = 3t - 5$
M1 for grouping $t$ terms on one side, e.g. $2w + 5 = t(3 - w)$
A1 for $t = \frac{2w+5}{3-w}$ or equivalent
Question 11 · short_answer
3 marks
Two mathematically similar cylinders have volumes of $54\pi\text{ cm}^3$ and $128\pi\text{ cm}^3$.
The total surface area of the smaller cylinder is $36\pi\text{ cm}^2$.

Calculate the total surface area of the larger cylinder.
Give your answer in terms of $\pi$.
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Worked solution

Let the scale factor for the volumes be $\frac{V_2}{V_1}$:
$$\frac{V_2}{V_1} = \frac{128\pi}{54\pi} = \frac{64}{27}$$

The linear scale factor $k$ is the cube root of the volume scale factor:
$$k = \sqrt[3]{\frac{64}{27}} = \frac{4}{3}$$

The area scale factor is $k^2$:
$$k^2 = \left(\frac{4}{3}\right)^2 = \frac{16}{9}$$

Therefore, the total surface area of the larger cylinder $A_2$ is:
$$A_2 = A_1 \times k^2 = 36\pi \times \frac{16}{9} = 4\pi \times 16 = 64\pi\text{ cm}^2$$

Marking scheme

M1 for volume ratio $\frac{128}{54}$ or linear scale factor $\sqrt[3]{\frac{128}{54}}$ or $\frac{4}{3}$ seen
M1 for area ratio $\left(\text{their } \frac{4}{3}\right)^2 = \frac{16}{9}$ seen
A1 for $64\pi$ or $201$ or $201.06...$
Question 12 · short_answer
3 marks
In triangle $ABC$, $AB = 7\text{ cm}$, $BC = 9\text{ cm}$ and angle $ABC = 64^\circ$.

Calculate the length of $AC$.
Give your answer correct to 3 significant figures.
Show answer & marking scheme

Worked solution

Using the Cosine Rule:
$$AC^2 = AB^2 + BC^2 - 2(AB)(BC)\cos(ABC)$$

Substitute the given values:
$$AC^2 = 7^2 + 9^2 - 2(7)(9)\cos(64^\circ)$$
$$AC^2 = 49 + 81 - 126\cos(64^\circ)$$
$$AC^2 = 130 - 126(0.43837...)$$
$$AC^2 \approx 130 - 55.235$$
$$AC^2 \approx 74.765$$
$$AC = \sqrt{74.765} \approx 8.6467\text{ cm}$$

Rounding to 3 significant figures gives $8.65\text{ cm}$.

Marking scheme

M1 for $7^2 + 9^2 - 2(7)(9)\cos(64^\circ)$
A1 for $74.8$ or $74.76...$ seen as $AC^2$
A1 for $8.65$ or $8.646...$
Question 13 · short_answer
3 marks
A box contains 5 red pens and 3 blue pens.
Two pens are taken at random from the box, without replacement.

Find the probability that at least one of the pens is blue.
Give your answer as a fraction in its simplest form.
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Worked solution

The total number of pens in the box is $5 + 3 = 8$.

Using the complement rule, the probability of choosing at least one blue pen is:
$$\text{P(at least one blue)} = 1 - \text{P(both red)}$$

The probability that both pens are red (without replacement) is:
$$\text{P(both red)} = \frac{5}{8} \times \frac{4}{7} = \frac{20}{56} = \frac{5}{14}$$

Therefore:
$$\text{P(at least one blue)} = 1 - \frac{5}{14} = \frac{9}{14}$$

Marking scheme

M1 for $\frac{5}{8} \times \frac{4}{7}$ oe
M1 for $1 - \text{their } P(\text{both red})$
A1 for $\frac{9}{14}$
Question 14 · short_answer
3 marks
Triangle $P$ is mapped onto Triangle $Q$ by a reflection in the line $y = -x$.
Triangle $Q$ is then mapped onto Triangle $R$ by a translation by the vector $\begin{pmatrix} 2 \\ -3 \end{pmatrix}$.

The coordinates of a vertex of Triangle $P$ are $(1, 4)$.

Find the coordinates of the corresponding vertex of Triangle $R$.
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Worked solution

First, reflect the vertex $(1, 4)$ in the line $y = -x$.
The general mapping for reflection in the line $y = -x$ is $(x, y) \rightarrow (-y, -x)$.
Therefore, the image of $(1, 4)$ is:
$$(-4, -1)$$

Next, apply the translation by the vector $\begin{pmatrix} 2 \\ -3 \end{pmatrix}$ to $(-4, -1)$:
$$\begin{pmatrix} -4 \\ -1 \end{pmatrix} + \begin{pmatrix} 2 \\ -3 \end{pmatrix} = \begin{pmatrix} -4 + 2 \\ -1 - 3 \end{pmatrix} = \begin{pmatrix} -2 \\ -4 \end{pmatrix}$$

So, the coordinates of the corresponding vertex of Triangle $R$ are $(-2, -4)$.

Marking scheme

M1 for finding coordinates of $Q$ as $(-4, -1)$ or for applying $(x, y) \rightarrow (-y, -x)$
M1 for adding $\begin{pmatrix} 2 \\ -3 \end{pmatrix}$ to their coordinates of $Q$
A1 for $(-2, -4)$
Question 15 · short_answer
3 marks
Evaluate
$$\frac{4.2 \times 10^7 + 1.8 \times 10^6}{2.5 \times 10^{-3}}$$
Give your answer in standard form.
Show answer & marking scheme

Worked solution

First, simplify the numerator by writing both terms with the same power of 10:
$$4.2 \times 10^7 = 42 \times 10^6$$
$$42 \times 10^6 + 1.8 \times 10^6 = 43.8 \times 10^6 = 4.38 \times 10^7$$

Next, divide by the denominator:
$$\frac{4.38 \times 10^7}{2.5 \times 10^{-3}} = \frac{4.38}{2.5} \times 10^{7 - (-3)} = 1.752 \times 10^{10}$$

Marking scheme

M1 for $4.38 \times 10^7$ seen in the numerator or $43.8 \times 10^6$
M1 for dividing $4.38$ by $2.5$ and applying index subtraction laws
A1 for $1.752 \times 10^{10}$
Question 16 · short_answer
3 marks
The position vector of point $A$ is $\mathbf{a} = \begin{pmatrix} 3 \\ -2 \end{pmatrix}$ and the position vector of point $B$ is $\mathbf{b} = \begin{pmatrix} -1 \\ 6 \end{pmatrix}$.

Find the vector $\overrightarrow{AB}$ as a column vector.
Show answer & marking scheme

Worked solution

The vector $\overrightarrow{AB}$ is given by:
$$\overrightarrow{AB} = \mathbf{b} - \mathbf{a}$$

Substitute the given column vectors:
$$\overrightarrow{AB} = \begin{pmatrix} -1 \\ 6 \end{pmatrix} - \begin{pmatrix} 3 \\ -2 \end{pmatrix} = \begin{pmatrix} -1 - 3 \\ 6 - (-2) \end{pmatrix} = \begin{pmatrix} -4 \\ 8 \end{pmatrix}$$

Marking scheme

M1 for $\mathbf{b} - \mathbf{a}$ seen as a vector subtraction, e.g. $\begin{pmatrix} -1 \\ 6 \end{pmatrix} - \begin{pmatrix} 3 \\ -2 \end{pmatrix}$
B1 for top value $-4$ or bottom value $8$
A1 for $\begin{pmatrix} -4 \\ 8 \end{pmatrix}$
Question 17 · short_answer
3 marks
The price of a laptop is reduced by 15% in a sale. The sale price is $646. Calculate the original price of the laptop.
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Worked solution

Let the original price of the laptop be \(x\).
Since the price is reduced by 15%, the sale price represents 85% of the original price.
\[0.85 \times x = 646\]
\[x = \frac{646}{0.85}\]
\[x = 760\]
Thus, the original price of the laptop is $760.

Marking scheme

M1 for \(0.85 \times x = 646\) or equivalent
M1 for \(\frac{646}{0.85}\)
A1 for 760
Question 18 · short_answer
3 marks
A solid metal sphere has radius 3 cm. It is melted down and recast into a solid cylinder of height 4 cm. Calculate the radius of the cylinder.
Show answer & marking scheme

Worked solution

First, calculate the volume of the sphere:
\[V_{\text{sphere}} = \frac{4}{3} \pi r^3 = \frac{4}{3} \pi (3)^3 = 36\pi \text{ cm}^3\]

Next, express the volume of the cylinder in terms of its radius \(R\):
\[V_{\text{cylinder}} = \pi R^2 h = \pi R^2 (4) = 4\pi R^2\]

Since the volume remains constant during melting and recasting:
\[4\pi R^2 = 36\pi\]
\[R^2 = 9\]
\[R = 3\text{ cm}\]
Thus, the radius of the cylinder is 3 cm.

Marking scheme

M1 for volume of sphere = \(\frac{4}{3}\pi (3)^3\) or \(36\pi\)
M1 for equating their sphere volume to \(\pi R^2 (4)\)
A1 for 3
Question 19 · short_answer
3 marks
A bag contains 5 red balls and 4 blue balls. Two balls are picked at random from the bag without replacement. Find the probability that the two balls are of different colours. Give your answer as a fraction in its simplest form.
Show answer & marking scheme

Worked solution

The total number of balls is \(5 + 4 = 9\).
The two ways to pick balls of different colours are (Red then Blue) or (Blue then Red).

\[P(\text{Red then Blue}) = \frac{5}{9} \times \frac{4}{8} = \frac{20}{72}\]
\[P(\text{Blue then Red}) = \frac{4}{9} \times \frac{5}{8} = \frac{20}{72}\]

Adding these two mutually exclusive probabilities:
\[P(\text{Different colours}) = \frac{20}{72} + \frac{20}{72} = \frac{40}{72} = \frac{5}{9}\]

Marking scheme

M1 for \(\frac{5}{9} \times \frac{4}{8}\) or \(\frac{4}{9} \times \frac{5}{8}\)
M1 for \(\frac{20}{72} + \frac{20}{72}\) or equivalent
A1 for \(\frac{5}{9}\)
Question 20 · short_answer
3 marks
Simplify \(\frac{2x^2 - 8}{x^2 + 3x - 10}\).
Show answer & marking scheme

Worked solution

Factorise the numerator:
\[2x^2 - 8 = 2(x^2 - 4) = 2(x - 2)(x + 2)\]

Factorise the denominator:
\[x^2 + 3x - 10 = (x + 5)(x - 2)\]

Simplify the fraction by cancelling out the common factor \((x - 2)\):
\[\frac{2(x - 2)(x + 2)}{(x + 5)(x - 2)} = \frac{2(x + 2)}{x + 5}\]

Marking scheme

B1 for factorising the numerator to \(2(x - 2)(x + 2)\)
B1 for factorising the denominator to \((x + 5)(x - 2)\)
B1 for final answer \(\frac{2(x+2)}{x+5}\) or equivalent
Question 21 · short_answer
3 marks
A ladder of length 5.5 m leans against a vertical wall. The foot of the ladder is 1.8 m from the base of the wall. Calculate the angle that the ladder makes with the horizontal ground. Give your answer correct to 1 decimal place.
Show answer & marking scheme

Worked solution

The ladder, wall, and ground form a right-angled triangle where the ladder is the hypotenuse (5.5 m) and the distance from the foot of the ladder to the wall is the adjacent side (1.8 m).
Let \(\theta\) be the angle between the ladder and the horizontal ground.
\[\cos\theta = \frac{1.8}{5.5}\]
\[\theta = \arccos\left(\frac{1.8}{5.5}\right) \approx 70.898^\circ\]
Rounding to 1 decimal place, we get \(70.9^\circ\).

Marking scheme

M1 for \(\cos\theta = \frac{1.8}{5.5}\) or equivalent
M1 for \(\theta = \arccos\left(\frac{1.8}{5.5}\right)\)
A1 for 70.9
Question 22 · short_answer
3 marks
In triangle \(ABC\), \(AB = 7\text{ cm}\), \(BC = 9\text{ cm}\) and angle \(ABC = 64^\circ\). Calculate the length of \(AC\). Give your answer correct to 3 significant figures.
Show answer & marking scheme

Worked solution

Using the cosine rule:
\[AC^2 = AB^2 + BC^2 - 2 \times AB \times BC \times \cos(ABC)\]
\[AC^2 = 7^2 + 9^2 - 2 \times 7 \times 9 \times \cos(64^\circ)\]
\[AC^2 = 49 + 81 - 126 \times \cos(64^\circ)\]
\[AC^2 \approx 130 - 126 \times 0.43837 = 130 - 55.2348 = 74.7652\]
\[AC = \sqrt{74.7652} \approx 8.6467\text{ cm}\]
To 3 significant figures, \(AC = 8.65\text{ cm}\).

Marking scheme

M1 for substituting correctly into the cosine rule: \(7^2 + 9^2 - 2(7)(9)\cos(64^\circ)\)
A1 for \(AC^2 \approx 74.8\) or better
A1 for 8.65
Question 23 · short_answer
3 marks
A curve has the equation \(y = 2x^3 - 9x^2 + 12x - 5\). Find the coordinates of the local minimum point of this curve.
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Worked solution

To find the stationary points, find the derivative \(\frac{dy}{dx}\) and set it to 0:
\[\frac{dy}{dx} = 6x^2 - 18x + 12\]
\[6x^2 - 18x + 12 = 0\]
\[6(x^2 - 3x + 2) = 0\]
\[6(x - 1)(x - 2) = 0\]
So the stationary points are at \(x = 1\) and \(x = 2\).

To determine which point is the local minimum, use the second derivative test:
\[\frac{d^2y}{dx^2} = 12x - 18\]
At \(x = 1\): \(\frac{d^2y}{dx^2} = 12(1) - 18 = -6 < 0\) (local maximum).
At \(x = 2\): \(\frac{d^2y}{dx^2} = 12(2) - 18 = 6 > 0\) (local minimum).

Find the \(y\)-coordinate at \(x = 2\):
\[y = 2(2)^3 - 9(2)^2 + 12(2) - 5 = 16 - 36 + 24 - 5 = -1\]
Thus, the coordinates of the local minimum point are \((2, -1)\).

Marking scheme

M1 for \(\frac{dy}{dx} = 6x^2 - 18x + 12\)
M1 for setting \(\frac{dy}{dx} = 0\) and solving to find stationary points at \(x = 1, x = 2\)
A1 for \((2, -1)\)
Question 24 · short_answer
3 marks
A cuboid has length 5 cm, width 6 cm and height 8 cm. Calculate the length of the diagonal of the cuboid. Give your answer correct to 3 significant figures.
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Worked solution

The diagonal of a cuboid with length \(l\), width \(w\), and height \(h\) is calculated using the 3D Pythagoras' theorem:
\[d = \sqrt{l^2 + w^2 + h^2}\]
\[d = \sqrt{5^2 + 6^2 + 8^2}\]
\[d = \sqrt{25 + 36 + 64} = \sqrt{125} \approx 11.18\text{ cm}\]
To 3 significant figures, \(d = 11.2\text{ cm}\).

Marking scheme

M1 for \(5^2 + 6^2 + 8^2\)
M1 for \(\sqrt{125}\) or better
A1 for 11.2
Question 25 · short_answer
3 marks
Find the equation of the line perpendicular to the line \(y = 3x - 5\) which passes through the point \((6, 2)\). Give your answer in the form \(y = mx + c\).
Show answer & marking scheme

Worked solution

The gradient of the line \(y = 3x - 5\) is \(3\). The gradient of the perpendicular line, \(m\), is given by the negative reciprocal: \(m = -\frac{1}{3}\). Using the equation of a straight line, \(y = mx + c\), we substitute the gradient and the point \((6, 2)\): \(2 = -\frac{1}{3}(6) + c\), which simplifies to \(2 = -2 + c\), giving \(c = 4\). Therefore, the equation of the perpendicular line is \(y = -\frac{1}{3}x + 4\).

Marking scheme

M1 for gradient of perpendicular line \(= -\frac{1}{3}\)
M1 for substituting \((6, 2)\) into \(y = mx + c\) with their perpendicular gradient
A1 for \(y = -\frac{1}{3}x + 4\) or equivalent
Question 26 · short_answer
2 marks
Simplify \(\left(64y^{12}\right)^{\frac{2}{3}}\).
Show answer & marking scheme

Worked solution

We apply the fractional power to each part of the term: \(\left(64y^{12}\right)^{\frac{2}{3}} = 64^{\frac{2}{3}} \times \left(y^{12}\right)^{\frac{2}{3}}\). First, evaluate the coefficient: \(64^{\frac{2}{3}} = (\sqrt[3]{64})^2 = 4^2 = 16\). Next, simplify the index of \(y\): \((y^{12})^{\frac{2}{3}} = y^{12 \times \frac{2}{3}} = y^8\). Combining these terms gives \(16y^8\).

Marking scheme

B1 for \(16\) or \(y^8\) in the final answer
or M1 for \(64^{\frac{2}{3}}\) evaluated as \(16\) or \(\left(y^{12}\right)^{\frac{2}{3}} = y^8\)

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Practice This Topic

Paper 42 Extended

Answer all questions. Show all necessary working clearly. Answers to non-exact values should be given to 3 significant figures.
11 Question · 131 marks
Question 1 · structured_multipart
13 marks
Liam bought a car and its value changes.

(a) The value of Liam's car today is $12 150. This is a decrease of 10% on the value last year. Calculate the value of the car last year. [2]

(b) The value of the car decreases by 8% each year of its value today. Calculate the value of the car after 3 years. [2]

(c) Liam invests $8000 at a rate of r% per year compound interest. At the end of 6 years, the value of the investment is $9850. Find the value of r. [3]

(d) A radioactive isotope decreases exponentially at a rate of 4.5% per hour.
(i) Find the overall percentage decrease in the mass of the isotope after 12 hours. [3]
(ii) Find the number of whole hours it takes for the mass of the isotope to be less than 40% of its original mass. [3]
Show answer & marking scheme

Worked solution

(a) Value last year = 12150 / 0.9 = $13500.

(b) Value after 3 years = 12150 * (0.92)^3 = 12150 * 0.778688 = $9461.06, which rounds to $9460 (to 3 significant figures).

(c) 8000 * (1 + r/100)^6 = 9850
(1 + r/100)^6 = 1.23125
1 + r/100 = 1.23125^(1/6) ≈ 1.035305
r = 3.53% (to 3 significant figures).

(d)(i) Let M_0 be the initial mass. Mass after 12 hours = M_0 * (1 - 0.045)^12 = M_0 * (0.955)^12 ≈ 0.57413 * M_0.
Overall percentage decrease = (1 - 0.57413) * 100% = 42.587% ≈ 42.6%.

(ii) (0.955)^t < 0.40
t * ln(0.955) < ln(0.40)
t * (-0.046044) < -0.91629
t > 19.9 hours.
Therefore, the number of whole hours is 20.

Marking scheme

(a) M1 for 12150 / 0.90, A1 for 13500.
(b) M1 for 12150 * (0.92)^3, A1 for 9460.
(c) M1 for (1 + r/100)^6 = 9850 / 8000, M1 for 1.23125^(1/6), A1 for 3.53.
(d)(i) M1 for (0.955)^12, A1 for 0.574 or 57.4%, A1 for 42.6%.
(d)(ii) M1 for (0.955)^t = 0.40 or trial and error with at least two values, A1 for 19.9, A1 for 20.
Question 2 · structured_multipart
12 marks
(a) A sector of a circle of radius 12 cm has a sector angle of y°. The sector is folded to form a cone with a base radius of 3.2 cm.
(i) Calculate the value of y. [3]
(ii) Calculate the height of the cone. [2]
(iii) Calculate the volume of the cone. [2]

(b) A solid metal cylinder has radius 6 cm and height 15 cm. It is melted down and recast into solid spheres, each of radius 2.5 cm. Calculate the maximum number of complete spheres that can be made. [3]

(c) Calculate the total surface area of one of the spheres. [2]
Show answer & marking scheme

Worked solution

(a)(i) Arc length of sector = 2 * pi * 12 * (y / 360).
Circumference of cone base = 2 * pi * 3.2.
2 * pi * 12 * (y / 360) = 2 * pi * 3.2
12 * y / 360 = 3.2
y = (3.2 * 360) / 12 = 96.

(a)(ii) Slant height of cone, l = 12 cm. Base radius, r = 3.2 cm.
Height, h = √(12^2 - 3.2^2) = √(144 - 10.24) = √133.76 ≈ 11.565 cm, which rounds to 11.6 cm.

(a)(iii) Volume = (1/3) * pi * r^2 * h = (1/3) * pi * 3.2^2 * 11.565 ≈ 124.28 cm^3, which rounds to 124 cm^3.

(b) Volume of cylinder = pi * r^2 * h = pi * 6^2 * 15 = 540 * pi ≈ 1696.46 cm^3.
Volume of one sphere = (4/3) * pi * R^3 = (4/3) * pi * 2.5^3 = (50/3) * pi ≈ 65.45 cm^3.
Number of spheres = 540 * pi / ((50/3) * pi) = 1620 / 50 = 32.4.
Maximum number of complete spheres is 32.

(c) Surface area = 4 * pi * R^2 = 4 * pi * 2.5^2 = 25 * pi ≈ 78.5398 cm^2, which rounds to 78.5 cm^2.

Marking scheme

(a)(i) M1 for 2 * pi * 12 * (y / 360) = 2 * pi * 3.2, M1 for y = 3.2 * 30, A1 for 96.
(a)(ii) M1 for 12^2 - 3.2^2, A1 for 11.6.
(a)(iii) M1 for (1/3) * pi * 3.2^2 * (their h), A1 for 124.
(b) M1 for volume of cylinder = 540 * pi, M1 for volume of sphere = (50/3) * pi, A1 for 32.
(c) M1 for 4 * pi * 2.5^2, A1 for 78.5.
Question 3 · structured_multipart
12 marks
(a) An online retailer sells wireless earbuds.
The cost of a basic model is $x. The cost of a premium model is $(x + 10).
An electronics store spends $450 on basic models and $500 on premium models.
The total number of earbuds purchased is 50.
(i) Show that x^2 - 9x - 90 = 0. [4]
(ii) Factorise x^2 - 9x - 90. [2]
(iii) Find the cost of a basic model. [1]

(b) Solve the equation 4 / (y - 3) - 3 / (y + 2) = 1. Show all your working and give your answers correct to 2 decimal places. [5]
Show answer & marking scheme

Worked solution

(a)(i) Number of basic models = 450 / x
Number of premium models = 500 / (x + 10)
Total earbuds = 450 / x + 500 / (x + 10) = 50.
Divide the equation by 50:
9 / x + 10 / (x + 10) = 1
Multiply by x(x + 10):
9(x + 10) + 10x = x(x + 10)
9x + 90 + 10x = x^2 + 10x
19x + 90 = x^2 + 10x
x^2 - 9x - 90 = 0.

(a)(ii) We look for two numbers that multiply to -90 and add to -9. These are -15 and 6.
Thus, x^2 - 9x - 90 = (x - 15)(x + 6).

(a)(iii) x = 15 or x = -6. Since cost must be positive, the cost of a basic model is $15.

(b) 4(y + 2) - 3(y - 3) = (y - 3)(y + 2)
4y + 8 - 3y + 9 = y^2 - y - 6
y + 17 = y^2 - y - 6
y^2 - 2y - 23 = 0.
Using the quadratic formula:
y = (2 ± √((-2)^2 - 4 * 1 * (-23))) / 2
y = (2 ± √(4 + 92)) / 2
y = (2 ± √96) / 2
y = 1 ± √24
y ≈ 5.90 or y ≈ -3.90.

Marking scheme

(a)(i) M1 for 450/x + 500/(x+10) = 50, M1 for 9(x+10) + 10x, M1 for clearing fractions to get 19x + 90 = x^2 + 10x, A1 for completing the show that.
(a)(ii) M1 for (x + a)(x + b) where ab = -90 or a + b = -9, A1 for (x - 15)(x + 6).
(a)(iii) B1 for 15.
(b) M1 for 4(y+2) - 3(y-3), M1 for (y-3)(y+2) = y^2 - y - 6, M1 for simplifying to y^2 - 2y - 23 = 0, B1 for √96 seen, A1 for 5.90 and -3.90.
Question 4 · structured_multipart
12 marks
A vertical flagpole, AB, stands on horizontal ground, with A at the base and B at the top.
Three points, C, D, and E are on the ground.
AC = 12 m, AD = 15 m, and angle CAD = 42°.

(a) Calculate the distance CD. [3]

(b) The height of the flagpole AB is 8.4 m.
(i) Calculate the angle of elevation of B (the top of the flagpole) from C. [2]
(ii) Calculate the distance from B to D. [3]
(iii) A straight wire is to be connected from B to a point P on the line CD such that the length of the wire BP is as short as possible. Calculate the length of this wire. [4]
Show answer & marking scheme

Worked solution

(a) Using the cosine rule on triangle CAD:
CD^2 = 12^2 + 15^2 - 2 * 12 * 15 * cos(42°)
CD^2 = 144 + 225 - 360 * 0.74314
CD^2 = 369 - 267.53 = 101.47
CD = √101.47 ≈ 10.073 m, which rounds to 10.1 m.

(b)(i) AB is vertical, so triangle BAC is right-angled at A.
tan(angle BCA) = AB / AC = 8.4 / 12 = 0.7
angle BCA = tan^-1(0.7) ≈ 34.99°, which rounds to 35.0°.

(b)(ii) AB is vertical, so triangle BAD is right-angled at A.
BD^2 = AB^2 + AD^2 = 8.4^2 + 15^2 = 70.56 + 225 = 295.56
BD = √295.56 ≈ 17.19 m, which rounds to 17.2 m.

(b)(iii) For the wire BP to be as short as possible, BP must be perpendicular to CD. Since AB is vertical, BP^2 = AB^2 + AP^2.
BP is minimised when AP is minimised, which means AP is perpendicular to CD on the ground.
Area of triangle CAD = 0.5 * AC * AD * sin(42°) = 0.5 * 12 * 15 * sin(42°) = 90 * 0.66913 = 60.222 m^2.
Also, Area of triangle CAD = 0.5 * CD * AP = 0.5 * 10.073 * AP.
60.222 = 5.0365 * AP
AP = 11.957 m.
Now, BP^2 = AB^2 + AP^2 = 8.4^2 + 11.957^2 = 70.56 + 142.97 = 213.53
BP = √213.53 ≈ 14.61 m, which rounds to 14.6 m.

Marking scheme

(a) M1 for 12^2 + 15^2 - 2 * 12 * 15 * cos(42°), A1 for 101.5, A1 for 10.1.
(b)(i) M1 for tan(theta) = 8.4 / 12, A1 for 35.0.
(b)(ii) M1 for 8.4^2 + 15^2, A1 for 295.56, A1 for 17.2.
(b)(iii) M1 for Area of CAD = 0.5 * 12 * 15 * sin(42°), M1 for AP = Area / (0.5 * 10.073) ≈ 11.96, M1 for BP^2 = 8.4^2 + AP^2, A1 for 14.6.
Question 5 · structured_multipart
12 marks
The diagram shows a field PQRS in the shape of a quadrilateral.
It is split into two triangles by the diagonal PR.
In triangle PQR: PQ = 45 m, QR = 62 m, and angle PQR = 108°.
In triangle PSR: angle SPR = 38° and angle PRS = 47°.

(a) Calculate the length of the diagonal PR. [3]
(b) Calculate the area of triangle PQR. [2]
(c) Calculate the length of SR. [3]
(d) Calculate the length of PS. [3]
(e) Calculate the perimeter of the field PQRS. [1]
Show answer & marking scheme

Worked solution

(a) Using the cosine rule on triangle PQR:
PR^2 = PQ^2 + QR^2 - 2 * PQ * QR * cos(108°)
PR^2 = 45^2 + 62^2 - 2 * 45 * 62 * cos(108°)
PR^2 = 2025 + 3844 - 5580 * (-0.30902)
PR^2 = 5869 + 1724.33 = 7593.33
PR = √7593.33 ≈ 87.14 m, which rounds to 87.1 m.

(b) Area of PQR = 0.5 * PQ * QR * sin(108°)
Area = 0.5 * 45 * 62 * sin(108°) = 1395 * 0.95106 ≈ 1326.7 m^2, which rounds to 1330 m^2.

(c) In triangle PSR, angle PSR = 180° - 38° - 47° = 95°.
Using the sine rule:
SR / sin(38°) = PR / sin(95°)
SR = 87.14 * sin(38°) / sin(95°)
SR = 87.14 * 0.61566 / 0.99619 ≈ 53.85 m, which rounds to 53.9 m.

(d) Using the sine rule on triangle PSR:
PS / sin(47°) = PR / sin(95°)
PS = 87.14 * sin(47°) / sin(95°)
PS = 87.14 * 0.73135 / 0.99619 ≈ 63.97 m, which rounds to 64.0 m.

(e) Perimeter = PQ + QR + SR + PS = 45 + 62 + 53.85 + 63.97 = 224.82 m, which rounds to 225 m.

Marking scheme

(a) M1 for 45^2 + 62^2 - 2 * 45 * 62 * cos(108°), A1 for 7593, A1 for 87.1.
(b) M1 for 0.5 * 45 * 62 * sin(108°), A1 for 1330.
(c) M1 for angle PSR = 95°, M1 for SR / sin(38°) = PR / sin(95°), A1 for 53.9.
(d) M1 for PS / sin(47°) = PR / sin(95°), A1 for 64.0.
(e) B1 for 225.
Question 6 · structured_multipart
12 marks
An urn contains 8 blue balls and 4 red balls.

(a) Two balls are chosen at random, without replacement.
A ball is chosen at random and its colour is recorded. It is not replaced. A second ball is then chosen at random and its colour is recorded.
Calculate the probability that:
(i) both balls are blue, [2]
(ii) the two balls have different colours, [3]
(iii) at least one ball is red. [2]

(b) A third ball is now chosen at random without replacement from the remaining 10 balls.
Calculate the probability that all three balls chosen are of the same colour. [3]

(c) Given that the first two balls chosen were of different colours, find the probability that the first ball was blue. [2]
Show answer & marking scheme

Worked solution

(a)(i) P(both blue) = P(Blue first) * P(Blue second | Blue first) = (8/12) * (7/11) = 56 / 132 = 14/33 ≈ 0.424.

(a)(ii) P(different colours) = P(Blue then Red) + P(Red then Blue)
= (8/12) * (4/11) + (4/12) * (8/11) = 32/132 + 32/132 = 64/132 = 16/33 ≈ 0.485.

(a)(iii) P(at least one red) = 1 - P(no red) = 1 - P(both blue) = 1 - 14/33 = 19/33 ≈ 0.576.

(b) P(three same) = P(B, B, B) + P(R, R, R)
P(B, B, B) = (8/12) * (7/11) * (6/10) = 336 / 1320
P(R, R, R) = (4/12) * (3/11) * (2/10) = 24 / 1320
P(three same) = (336 + 24) / 1320 = 360 / 1320 = 3/11 ≈ 0.273.

(c) We are given the first two balls have different colours: {BR, RB}.
P(First was Blue | Different) = P(BR) / (P(BR) + P(RB)) = (32/132) / (64/132) = 32 / 64 = 0.5.

Marking scheme

(a)(i) M1 for (8/12) * (7/11), A1 for 14/33 (or 0.424).
(a)(ii) M1 for (8/12) * (4/11), M1 for (4/12) * (8/11) + (8/12) * (4/11), A1 for 16/33 (or 0.485).
(a)(iii) M1 for 1 - (their (a)(i)), A1 for 19/33 (or 0.576).
(b) M1 for (8/12) * (7/11) * (6/10), M1 for (4/12) * (3/11) * (2/10), A1 for 3/11 (or 0.273).
(c) M1 for (32/132) / (64/132) or equivalent logic, A1 for 0.5 (or 1/2).
Question 7 · structured_multipart
12 marks
The equation of a curve is y = 2x^3 - 9x^2 - 24x + 10.

(a) Find dy/dx. [2]

(b) Find the coordinates of the two stationary points of the curve. [4]

(c) Determine the nature of each stationary point. Show your working clearly. [3]

(d) Find the equation of the tangent to the curve at the point where x = 2. Give your answer in the form y = mx + c. [3]
Show answer & marking scheme

Worked solution

(a) dy/dx = d/dx (2x^3 - 9x^2 - 24x + 10) = 6x^2 - 18x - 24.

(b) Stationary points occur when dy/dx = 0:
6x^2 - 18x - 24 = 0
x^2 - 3x - 4 = 0
(x - 4)(x + 1) = 0
So x = 4 or x = -1.

When x = 4:
y = 2(4)^3 - 9(4)^2 - 24(4) + 10 = 2(64) - 9(16) - 96 + 10 = 128 - 144 - 96 + 10 = -102.
The coordinate is (4, -102).

When x = -1:
y = 2(-1)^3 - 9(-1)^2 - 24(-1) + 10 = -2 - 9 + 24 + 10 = 23.
The coordinate is (-1, 23).

(c) Find the second derivative:
d^2y/dx^2 = 12x - 18.
At x = 4:
d^2y/dx^2 = 12(4) - 18 = 30 > 0. Since the second derivative is positive, (4, -102) is a local minimum.
At x = -1:
d^2y/dx^2 = 12(-1) - 18 = -30 < 0. Since the second derivative is negative, (-1, 23) is a local maximum.

(d) At x = 2:
y = 2(2)^3 - 9(2)^2 - 24(2) + 10 = 16 - 36 - 48 + 10 = -58.
The gradient of the tangent, m, is the value of dy/dx at x = 2:
m = 6(2)^2 - 18(2) - 24 = 24 - 36 - 24 = -36.
The equation of the tangent is:
y - y1 = m(x - x1)
y - (-58) = -36(x - 2)
y + 58 = -36x + 72
y = -36x + 14.

Marking scheme

(a) B2 for 6x^2 - 18x - 24 (B1 for 6x^2 or -18x or -24).
(b) M1 for setting their dy/dx = 0, A1 for x = 4 and x = -1, A1 for y = -102, A1 for y = 23.
(c) M1 for finding d^2y/dx^2 = 12x - 18, A1 for evaluating d^2y/dx^2 at x = 4 and x = -1, A1 for correctly stating minimum and maximum.
(d) M1 for evaluating y = -58 at x = 2, M1 for evaluating gradient m = -36, A1 for y = -36x + 14.
Question 8 · structured_multipart
11 marks
Triangles A, B, C, and D are drawn on a grid.
Triangle A has vertices at (1, 2), (4, 2), and (4, 4).
Triangle B has vertices at (-1, 2), (-4, 2), and (-4, 4).
Triangle C has vertices at (1, -2), (4, -2), and (4, -4).
Triangle D has vertices at (2, 4), (8, 4), and (8, 8).

(a) Describe fully the single transformation that maps:
(i) Triangle A onto Triangle B, [2]
(ii) Triangle A onto Triangle C, [2]
(iii) Triangle A onto Triangle D. [3]

(b) Triangle A is mapped onto Triangle E by a rotation of 90° clockwise about the origin. Write down the coordinates of the vertices of Triangle E. [2]

(c) Triangle A is mapped onto Triangle F by a shear, with the x-axis invariant and shear factor 2. Write down the coordinates of the vertices of Triangle F. [2]
Show answer & marking scheme

Worked solution

(a)(i) Since the x-coordinates are negated and y-coordinates remain unchanged, this is a reflection in the y-axis (or the line x = 0).

(a)(ii) Since the y-coordinates are negated and x-coordinates remain unchanged, this is a reflection in the x-axis (or the line y = 0).

(a)(iii) Both x and y coordinates are multiplied by 2. This is an enlargement with scale factor 2 and the centre of enlargement is the origin (0, 0).

(b) A rotation of 90° clockwise about the origin transforms (x, y) to (y, -x).
- (1, 2) becomes (2, -1)
- (4, 2) becomes (2, -4)
- (4, 4) becomes (4, -4)
The vertices of Triangle E are (2, -1), (2, -4), and (4, -4).

(c) A shear with the x-axis invariant and shear factor 2 transforms (x, y) to (x + 2y, y).
- (1, 2) becomes (1 + 2*2, 2) = (5, 2)
- (4, 2) becomes (4 + 2*2, 2) = (8, 2)
- (4, 4) becomes (4 + 2*4, 4) = (12, 4)
The vertices of Triangle F are (5, 2), (8, 2), and (12, 4).

Marking scheme

(a)(i) B1 for Reflection, B1 for the y-axis (or line x = 0).
(a)(ii) B1 for Reflection, B1 for the x-axis (or line y = 0).
(a)(iii) B1 for Enlargement, B1 for scale factor 2, B1 for centre (0, 0).
(b) M1 for any two coordinates correct, A1 for all three correct: (2, -1), (2, -4), (4, -4).
(c) M1 for use of (x + 2y, y) or finding two vertices correctly, A1 for all three correct: (5, 2), (8, 2), (12, 4).
Question 9 · structured_multipart
12 marks
A communication tower, $T$, stands vertically on the slope of a hill.
Two monitoring points, $A$ and $B$, are on the horizontal ground at the foot of the hill.

(a) The distance between $A$ and $B$ is 150 m. The bearing of $B$ from $A$ is $075^\circ$.
A third point $C$ is on the horizontal ground such that the distance $AC = 120$ m and the distance $BC = 180$ m.

(i) Show that angle $ACB = 55.8^\circ$, correct to 1 decimal place.

(ii) Find the bearing of $C$ from $A$, given that the bearing of $C$ from $A$ is between $090^\circ$ and $180^\circ$.

(b) The base of the tower is at point $D$ on the hillside, which is vertically above $C$ at a height of 25 m. The tower $TD$ has a height of 40 m.

(i) Calculate the distance from $A$ to the top of the tower, $T$.

(ii) Calculate the angle of elevation of $T$ from $B$.
Show answer & marking scheme

Worked solution

(a)(i) Using the cosine rule in triangle $ABC$:
$$\cos \angle ACB = \frac{AC^2 + BC^2 - AB^2}{2 \cdot AC \cdot BC}$$
$$\cos \angle ACB = \frac{120^2 + 180^2 - 150^2}{2 \cdot 120 \cdot 180}$$
$$\cos \angle ACB = \frac{14400 + 32400 - 22500}{43200} = \frac{24300}{43200} = 0.5625$$
$$\angle ACB = \arccos(0.5625) \approx 55.771^\circ$$
Rounding to 1 decimal place gives $55.8^\circ$.

(a)(ii) First, find the angle $CAB$ using the cosine rule:
$$\cos \angle CAB = \frac{AC^2 + AB^2 - BC^2}{2 \cdot AC \cdot AB}$$
$$\cos \angle CAB = \frac{120^2 + 150^2 - 180^2}{2 \cdot 120 \cdot 150}$$
$$\cos \angle CAB = \frac{14400 + 22500 - 32400}{36000} = \frac{4500}{36000} = 0.125$$
$$\angle CAB = \arccos(0.125) \approx 82.819^\circ$$
Since the bearing of $C$ from $A$ is between $090^\circ$ and $180^\circ$, we add this angle to the bearing of $B$ from $A$:
$$\text{Bearing} = 75^\circ + 82.819^\circ = 157.819^\circ \approx 157.8^\circ$$

(b)(i) The top of the tower $T$ is vertically above $C$.
The height of $T$ above $C$ is the height of $D$ above $C$ plus the height of the tower $TD$:
$$TC = 25\text{ m} + 40\text{ m} = 65\text{ m}$$
Triangle $TAC$ is a right-angled triangle with the right angle at $C$:
$$AT = \sqrt{AC^2 + TC^2} = \sqrt{120^2 + 65^2} = \sqrt{14400 + 4225} = \sqrt{18625} \approx 136.47\text{ m}$$
Correct to 3 significant figures, $AT = 136\text{ m}$.

(b)(ii) Triangle $TBC$ is a right-angled triangle with the right angle at $C$.
Let $\theta$ be the angle of elevation of $T$ from $B$:
$$\tan \theta = \frac{TC}{BC} = \frac{65}{180}$$
$$\theta = \arctan\left(\frac{65}{180}\right) \approx 19.854^\circ$$
Correct to 3 significant figures, the angle of elevation is $19.9^\circ$.

Marking scheme

(a)(i) [3 marks]
M1 for $\cos \angle ACB = \frac{120^2 + 180^2 - 150^2}{2 \cdot 120 \cdot 180}$
A1 for $\cos \angle ACB = 0.5625$
A1 for $\arccos(0.5625) = 55.77...$ showing rounding to $55.8^\circ$

(a)(ii) [3 marks]
M1 for $\cos \angle CAB = \frac{120^2 + 150^2 - 180^2}{2 \cdot 120 \cdot 150}$
A1 for $\angle CAB = 82.8^\circ$ or $82.81...^\circ$
A1 for bearing $= 157.8^\circ$ or $158^\circ$

(b)(i) [4 marks]
B1 for $TC = 65$ seen or implied
M1 for $AT^2 = 120^2 + TC^2$
M1 for $\sqrt{120^2 + 65^2}$
A1 for $136$ or $136.47...$ (accept 136.5)

(b)(ii) [2 marks]
M1 for $\tan \theta = \frac{65}{180}$
A1 for $19.9^\circ$ or $19.85...^\circ$
Question 10 · structured_multipart
12 marks
A curve has the equation $y = 2x^3 - 9x^2 - 24x + 15$.

(a) Find $\frac{\mathrm{d}y}{\mathrm{d}x}$.

(b) Find the coordinates of the two stationary points on the curve.

(c) Determine the nature of each stationary point. Show your working clearly.

(d) Find the equation of the tangent to the curve at the point where $x = 1$. Give your answer in the form $y = mx + c$.
Show answer & marking scheme

Worked solution

(a) Differentiating $y = 2x^3 - 9x^2 - 24x + 15$ with respect to $x$:
$$\frac{\mathrm{d}y}{\mathrm{d}x} = 6x^2 - 18x - 24$$

(b) Stationary points occur when $\frac{\mathrm{d}y}{\mathrm{d}x} = 0$:
$$6x^2 - 18x - 24 = 0$$
Divide by 6:
$$x^2 - 3x - 4 = 0$$
$$(x - 4)(x + 1) = 0$$
So, $x = 4$ or $x = -1$.

When $x = 4$:
$$y = 2(4)^3 - 9(4)^2 - 24(4) + 15 = 128 - 144 - 96 + 15 = -97$$
Stationary point: $(4, -97)$.

When $x = -1$:
$$y = 2(-1)^3 - 9(-1)^2 - 24(-1) + 15 = -2 - 9 + 24 + 15 = 28$$
Stationary point: $(-1, 28)$.

(c) Using the second derivative to determine the nature:
$$\frac{\mathrm{d}^2y}{\mathrm{d}x^2} = 12x - 18$$

For $x = 4$:
$$\frac{\mathrm{d}^2y}{\mathrm{d}x^2} = 12(4) - 18 = 30 > 0$$
Since $\frac{\mathrm{d}^2y}{\mathrm{d}x^2} > 0$, the point $(4, -97)$ is a local minimum.

For $x = -1$:
$$\frac{\mathrm{d}^2y}{\mathrm{d}x^2} = 12(-1) - 18 = -30 < 0$$
Since $\frac{\mathrm{d}^2y}{\mathrm{d}x^2} < 0$, the point $(-1, 28)$ is a local maximum.

(d) Find the gradient of the tangent at $x = 1$:
$$m = 6(1)^2 - 18(1) - 24 = 6 - 18 - 24 = -36$$
Find the $y$-value at $x = 1$:
$$y = 2(1)^3 - 9(1)^2 - 24(1) + 15 = -16$$
The equation of the tangent is:
$$y - (-16) = -36(x - 1)$$
$$y + 16 = -36x + 36$$
$$y = -36x + 20$$

Marking scheme

(a) [2 marks]
B2 for $6x^2 - 18x - 24$ (B1 for two terms correct)

(b) [5 marks]
M1 for setting their derivative equal to 0
M1 for factorising/solving quadratic to find $x = 4$ and $x = -1$
A1 for $x = 4$ and $x = -1$
A1 for $y = -97$
A1 for $y = 28$

(c) [3 marks]
M1 for finding $\frac{\mathrm{d}^2y}{\mathrm{d}x^2} = 12x - 18$ (or using first-derivative method)
A1 for $(4, -97)$ is a minimum with explanation (e.g., $30 > 0$)
A1 for $(-1, 28)$ is a maximum with explanation (e.g., $-30 < 0$)

(d) [2 marks]
M1 for substituting $x = 1$ into derivative to get $m = -36$ and finding $y = -16$
A1 for $y = -36x + 20$ or equivalent
Question 11 · structured_multipart
11 marks
A bag contains 12 colored disks: 5 are Red, 4 are Blue, and 3 are Yellow.
Two disks are taken at random from the bag, one after the other, without replacement.

(a) Find the probability that:

(i) both disks are the same color,

(ii) the two disks are of different colors.

(b) A third disk is now taken at random from the remaining 10 disks in the bag, without replacement.
Find the probability that:

(i) the first disk is Red, the second is Blue, and the third is Yellow,

(ii) exactly two of the three disks are Red.
Show answer & marking scheme

Worked solution

(a)(i) The probability that both disks are the same color is the sum of the probabilities of choosing RR, BB, or YY:
$$P(RR) = \frac{5}{12} \times \frac{4}{11} = \frac{20}{132}$$
$$P(BB) = \frac{4}{12} \times \frac{3}{11} = \frac{12}{132}$$
$$P(YY) = \frac{3}{12} \times \frac{2}{11} = \frac{6}{132}$$
$$P(\text{same color}) = \frac{20 + 12 + 6}{132} = \frac{38}{132} = \frac{19}{66} \approx 0.288$$

(a)(ii) The probability that they are of different colors is:
$$P(\text{different colors}) = 1 - P(\text{same color}) = 1 - \frac{19}{66} = \frac{47}{66} \approx 0.712$$

(b)(i) The probability of selecting Red first, Blue second, and Yellow third is:
$$P(R_1 \text{ and } B_2 \text{ and } Y_3) = \frac{5}{12} \times \frac{4}{11} \times \frac{3}{10} = \frac{60}{1320} = \frac{1}{22} \approx 0.0455$$

(b)(ii) Exactly two of the three disks are Red. The possible sequences are RRX, RXR, and XRR, where X is a non-Red disk (7 non-Red disks originally):
$$P(RRX) = \frac{5}{12} \times \frac{4}{11} \times \frac{7}{10} = \frac{140}{1320}$$
$$P(RXR) = \frac{5}{12} \times \frac{7}{11} \times \frac{4}{10} = \frac{140}{1320}$$
$$P(XRR) = \frac{7}{12} \times \frac{5}{11} \times \frac{4}{10} = \frac{140}{1320}$$
$$P(\text{exactly two Red}) = 3 \times \frac{140}{1320} = \frac{420}{1320} = \frac{7}{22} \approx 0.318$$

Marking scheme

(a)(i) [3 marks]
M1 for any correct product of two probabilities (e.g. $\frac{5}{12} \times \frac{4}{11}$)
M1 for summing three correct products: $\frac{20}{132} + \frac{12}{132} + \frac{6}{132}$
A1 for $\frac{19}{66}$ or $0.288$ or $0.2878...$

(a)(ii) [2 marks]
M1 for $1 - \text{their } P(\text{same})$
A1 for $\frac{47}{66}$ or $0.712$ or $0.7121...$

(b)(i) [2 marks]
M1 for $\frac{5}{12} \times \frac{4}{11} \times \frac{3}{10}$
A1 for $\frac{1}{22}$ or $0.0455$ or $0.04545...$

(b)(ii) [4 marks]
M1 for the probability of one combination, e.g. $\frac{5}{12} \times \frac{4}{11} \times \frac{7}{10} = \frac{140}{1320}$
M1 for identifying there are 3 such combinations (RRX, RXR, XRR)
M1 for $3 \times \text{their product}$
A1 for $\frac{7}{22}$ or $0.318$ or $0.3181...$

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