An original Thinka practice paper modelled on the structure and difficulty of the Nov 2023 (V1) Cambridge IGCSE Mathematics (0580) paper. Not affiliated with or reproduced from Cambridge.
Paper 2 (Extended) - Short & Medium Structured
Answer all questions. Electronic calculators should be used. Working must be clearly shown.
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Worked solution
Divide the numerical parts and subtract the powers of 10: \[\frac{4.8}{1.5} = 3.2\] \[10^7 \div 10^{-3} = 10^{7 - (-3)} = 10^{10}\] Combining these gives \(3.2 \times 10^{10}\).
Marking scheme
M1 for \(\frac{4.8}{1.5}\) or \(10^{7 - (-3)}\) seen or \(32\,000\,000\,000\) A0.5 for \(3.2 \times 10^{10}\) cao
Question 2 · Short Answer
1.5 marks
Factorise completely. \[18x^3y - 8xy^3\]
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Worked solution
First factor out the highest common factor, \(2xy\): \[18x^3y - 8xy^3 = 2xy(9x^2 - 4y^2)\] Then factorise the difference of two squares: \[9x^2 - 4y^2 = (3x - 2y)(3x + 2y)\] Thus, the fully factorised form is \(2xy(3x - 2y)(3x + 2y)\).
Marking scheme
M1 for \(2xy(9x^2 - 4y^2)\) or for recognising difference of two squares \((3x - 2y)(3x + 2y)\) A0.5 for \(2xy(3x - 2y)(3x + 2y)\) oe
Question 3 · Short Answer
1.5 marks
A sector of a circle with radius \(7.5\text{ cm}\) has a sector angle of \(144^\circ\).
Calculate the perimeter of the sector.
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Worked solution
First calculate the arc length of the sector: \[\text{Arc length} = \frac{144}{360} \times 2 \times \pi \times 7.5 = \frac{2}{5} \times 15\pi = 6\pi \approx 18.8496\text{ cm}\] The perimeter includes the arc length plus two radii: \[\text{Perimeter} = 6\pi + 2(7.5) = 6\pi + 15 \approx 33.85\text{ cm} \text{ (or } 33.8\text{ to 3 s.f.)}\]
Marking scheme
M1 for \(\frac{144}{360} \times 2 \times \pi \times 7.5\) oe (soi by \(6\pi\) or \(18.8\dots\)) A0.5 for \(33.8\) or \(33.85\) or \(6\pi + 15\)
Question 4 · Short Answer
1.5 marks
The vector \(\mathbf{v} = \begin{pmatrix} k \\ -12 \end{pmatrix}\) has magnitude \(13\), where \(k > 0\).
Find the value of \(k\).
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Worked solution
The magnitude of the vector is given by: \[|\mathbf{v}| = \sqrt{k^2 + (-12)^2} = 13\] Square both sides: \[k^2 + 144 = 169\] \[k^2 = 25\] Since \(k > 0\), \(k = 5\).
Marking scheme
M1 for \(k^2 + (-12)^2 = 13^2\) oe A0.5 for \(5\) (do not accept \(\pm 5\))
Question 5 · Short Answer
1.5 marks
After a price reduction of \(15\%\), a jacket costs \(\$61.20\).
Calculate the original price of the jacket.
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Worked solution
The reduced price represents \(100\% - 15\% = 85\%\) of the original price. \[\text{Original price} = \frac{61.20}{0.85} = 72\]
Marking scheme
M1 for \(61.20 \div (1 - 0.15)\) or \(61.20 \div 0.85\) oe A0.5 for \(72\) or \(72.00\)
Question 6 · Short Answer
1.5 marks
Calculate \((4.8 \times 10^7) \div (1.5 \times 10^{-3})\). Give your answer in standard form.
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Worked solution
Divide the numerical coefficients and subtract the indices for the power of 10: \((4.8 \div 1.5) \times 10^{7 - (-3)} = 3.2 \times 10^{10}\).
Marking scheme
M1 for \(3.2 \times 10^k\) or \(k \times 10^{10}\) (where \(k \ne 3.2\)) or \(32\,000\,000\,000\). A0.5 for \(3.2 \times 10^{10}\) cao.
Question 7 · Short Answer
1.5 marks
Factorise completely. \(18x^2y - 24xy^3\)
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Worked solution
Identify the highest common factor of \(18x^2y\) and \(24xy^3\), which is \(6xy\). Dividing each term by \(6xy\) gives \(6xy(3x - 4y^2)\).
Marking scheme
M1 for any partial factorisation with at least two common factors extracted (e.g. \(3xy(6x - 8y^2)\) or \(6x(3xy - 4y^3)\) or \(6y(3x^2 - 4xy^2)\)). A0.5 for \(6xy(3x - 4y^2)\) cao.
Question 8 · Short Answer
1.5 marks
Find the \(n\)th term of the sequence \(7, 13, 19, 25, 31, \ldots\)
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Worked solution
The sequence has a constant first difference of \(d = 6\), so the rule starts with \(6n\). The zeroth term is \(7 - 6 = 1\). Therefore, the \(n\)th term is \(6n + 1\).
Marking scheme
M1 for \(6n + c\) (where \(c \ne 1\)) or \(6n\) seen. A0.5 for \(6n + 1\) oe.
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Worked solution
Use the magnitude formula for a vector: \(|\mathbf{v}| = \sqrt{(-8)^2 + 15^2} = \sqrt{64 + 225} = \sqrt{289} = 17\).
Marking scheme
M1 for \(\sqrt{(-8)^2 + 15^2}\) or \(\sqrt{64 + 225}\) or \(\sqrt{289}\). A0.5 for 17 cao.
Question 10 · Short Answer
1.5 marks
The length of a rectangular tile is \(24\text{ cm}\), correct to the nearest centimetre. The width is \(15\text{ cm}\), correct to the nearest centimetre. Calculate the upper bound for the perimeter of the tile.
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3. Collect like terms: \[ 5x - 4x + 20 + 6 = x + 26 \]
4. Combine into a single fraction: \[ \frac{x + 26}{(2x - 3)(x + 4)} \]
Marking scheme
M1 for writing over a common denominator \((2x - 3)(x + 4)\) with at least one numerator correct M1 for correct expansion of numerators, \(5x + 20 - 4x + 6\) soi A1 for \(\frac{x + 26}{(2x - 3)(x + 4)}\) or \(\frac{x + 26}{2x^2 + 5x - 12}\)
Question 12 · Structured Procedural
3 marks
A sector of a circle of radius \(7.5\text{ cm}\) has a perimeter of \(28.2\text{ cm}\).
Calculate the angle of the sector. Give your answer correct to 1 decimal place.
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Worked solution
1. The perimeter of a sector is given by: \[ \text{Perimeter} = 2r + \text{arc length} \] \[ 28.2 = 2(7.5) + \text{arc length} \] \[ \text{Arc length} = 28.2 - 15 = 13.2\text{ cm} \]
2. Use the arc length formula to find the angle \(\theta\): \[ \text{Arc length} = \frac{\theta}{360} \times 2\pi r \] \[ 13.2 = \frac{\theta}{360} \times 2 \times \pi \times 7.5 \] \[ 13.2 = \frac{15\pi\theta}{360} \]
Correct to 1 decimal place, \(\theta = 100.8^\circ\).
Marking scheme
M1 for \(28.2 - 2 \times 7.5\) or \(13.2\) soi M1 for \(\frac{\theta}{360} \times 2 \times \pi \times 7.5 = \text{their } 13.2\) oe A1 for \(100.8\) or \(100.84\dots\)
Question 13 · Structured Procedural
3 marks
Solve the equation.
\[ 27^{2x - 1} = \frac{1}{9\sqrt{3}} \]
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M1 for writing \(27^{2x - 1}\) as \(3^{3(2x - 1)}\) or \(3^{6x - 3}\) soi M1 for writing \(\frac{1}{9\sqrt{3}}\) as \(3^{-2.5}\) or \(3^{-\frac{5}{2}}\) soi A1 for \(\frac{1}{12}\) or \(0.0833\) or \(0.0833\dots\)
Question 14 · Structured Procedural
3 marks
A vehicle travels a distance of \(480\text{ m}\), correct to the nearest \(10\text{ m}\). The time taken is \(18.4\text{ s}\), correct to the nearest \(0.1\text{ s}\).
Calculate the upper bound for the average speed of the vehicle in \(\text{m/s}\). Give your answer correct to 3 significant figures.
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Worked solution
1. Determine the bounds for distance and time: - Distance: \(480\text{ m}\) to nearest \(10\text{ m}\) \(\implies \text{Upper bound} = 480 + 5 = 485\text{ m}\) - Time: \(18.4\text{ s}\) to nearest \(0.1\text{ s}\) \(\implies \text{Lower bound} = 18.4 - 0.05 = 18.35\text{ s}\)
2. Calculate the upper bound of speed: \[ \text{Upper bound of speed} = \frac{\text{Upper bound of distance}}{\text{Lower bound of time}} = \frac{485}{18.35} \]
Correct to 3 significant figures, the value is \(26.4\).
Marking scheme
B1 for \(485\) or \(18.35\) seen M1 for \(\frac{\text{UB of distance}}{\text{LB of time}}\) where \(480 < \text{UB} \le 485\) and \(18.35 \le \text{LB} < 18.4\) A1 for \(26.4\) or \(26.43\dots\)
Since the second difference is constant (\(4\)), the sequence is quadratic with leading term \(a n^2\): \[ 2a = 4 \implies a = 2 \]
3. Subtract \(2n^2\) from each term: - For \(n = 1\): \(3 - 2(1)^2 = 1\) - For \(n = 2\): \(11 - 2(2)^2 = 3\) - For \(n = 3\): \(23 - 2(3)^2 = 5\) - For \(n = 4\): \(39 - 2(4)^2 = 7\)
4. Find the \(n\)th term of the linear remainder \(1, 3, 5, 7, \dots\): \[ \text{Linear part} = 2n - 1 \]
5. Combine the parts: \[ T_n = 2n^2 + 2n - 1 \]
Marking scheme
M1 for second difference \(= 4\) soi, giving \(2n^2\) as the first term M1 for subtracting \(2n^2\) from the sequence terms to obtain \(1, 3, 5, 7, \dots\) oe A1 for \(2n^2 + 2n - 1\) oe
Question 16 · Structured Procedural
3 marks
Write as a single fraction in its simplest form.
\[ \frac{3}{2x - 1} - \frac{2}{x + 4} \]
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Worked solution
To subtract the algebraic fractions, find a common denominator: \[ \frac{3(x + 4) - 2(2x - 1)}{(2x - 1)(x + 4)} \]
Expand the brackets in the numerator: \[ 3(x + 4) = 3x + 12 \] \[ -2(2x - 1) = -4x + 2 \]
Combine like terms in the numerator: \[ 3x + 12 - 4x + 2 = 14 - x \]
Write the resulting fraction over the common denominator: \[ \frac{14 - x}{(2x - 1)(x + 4)} \]
Marking scheme
M1 for writing with a common denominator \((2x - 1)(x + 4)\) seen M1 for correct expansion of numerators: \(3(x + 4) - 2(2x - 1)\) or \(3x + 12 - 4x + 2\) soi A1 for \(\frac{14 - x}{(2x - 1)(x + 4)}\) or \(\frac{-x + 14}{(2x - 1)(x + 4)}\) or \(\frac{14 - x}{2x^2 + 7x - 4}\) oe
Question 17 · Structured Procedural
3 marks
A sector of a circle has radius \(7.5\text{ cm}\) and sector angle \(140^\circ\).
Calculate the perimeter of the sector.
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Worked solution
First, calculate the arc length of the sector: \[ \text{Arc length} = \frac{140}{360} \times 2 \times \pi \times 7.5 = \frac{7}{18} \times 15\pi = \frac{35\pi}{6} \approx 18.326\text{ cm} \]
Next, calculate the total perimeter by adding the two radii: \[ \text{Perimeter} = \text{Arc length} + 2r \] \[ \text{Perimeter} = 18.326 + 2 \times 7.5 = 18.326 + 15 = 33.326\text{ cm} \]
Rounding to 3 significant figures gives \(33.3\text{ cm}\).
Marking scheme
M1 for \(\frac{140}{360} \times 2 \times \pi \times 7.5\) oe M1 for \((\text{their arc length}) + 2 \times 7.5\) oe A1 for \(33.3\) or \(33.32\dots\) to \(33.33\) or \(\frac{35\pi}{6} + 15\)
Question 18 · Structured Procedural
3 marks
A rectangular field has length \(68\text{ m}\), correct to the nearest metre, and width \(42.4\text{ m}\), correct to 1 decimal place.
Calculate the upper bound for the area of the field.
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Worked solution
Identify the upper bound for each measurement: - Length is given to the nearest metre: \(\text{Upper bound of length} = 68 + 0.5 = 68.5\text{ m}\) - Width is given to 1 decimal place (nearest \(0.1\text{ m}\)): \(\text{Upper bound of width} = 42.4 + 0.05 = 42.45\text{ m}\)
Calculate the upper bound for the area by multiplying the upper bounds: \[ \text{Upper bound for area} = 68.5 \times 42.45 = 2907.825\text{ m}^2 \]
Marking scheme
B1 for \(68.5\) or \(42.45\) seen M1 for \((\text{their upper bound of length}) \times (\text{their upper bound of width})\) where \(68 < \text{UB of length} \le 68.5\) and \(42.4 < \text{UB of width} \le 42.45\) A1 for \(2907.825\) cao
Question 19 · Multi-Step Geometric / Algebraic
4 marks
Solve the equation.
\[\dfrac{2}{x - 1} + \dfrac{3}{x + 2} = 2\]
Show all your working.
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Worked solution
1. Multiply through by the common denominator \((x - 1)(x + 2)\): \[2(x + 2) + 3(x - 1) = 2(x - 1)(x + 2)\]
3. Rearrange into standard quadratic form \(ax^2 + bx + c = 0\): \[2x^2 - 3x - 5 = 0\]
4. Solve by factorising or using the quadratic formula: \[(2x - 5)(x + 1) = 0\]
\[2x - 5 = 0 \implies x = 2.5\] \[x + 1 = 0 \implies x = -1\]
Marking scheme
M1 for multiplying by common denominator to obtain \(2(x + 2) + 3(x - 1) = 2(x - 1)(x + 2)\) oe M1 for expanding and simplifying to a correct 3-term quadratic \(2x^2 - 3x - 5 = 0\) oe M1 for factorising \((2x - 5)(x + 1) = 0\) or correct substitution into the quadratic formula for their 3-term quadratic A1 for \(x = -1\) and \(x = 2.5\) (or \(\frac{5}{2}\) or \(2\frac{1}{2}\))
Question 20 · Multi-Step Geometric / Algebraic
5 marks
NOT TO SCALE
\(OAB\) is a sector of a circle with centre \(O\) and radius \(12\text{ cm}\). Angle \(AOB = 75^\circ\). \(C\) is a point on the arc \(AB\) such that angle \(AOC = 45^\circ\) and angle \(COB = 30^\circ\).
Calculate the area of the shaded region bounded by the chord \(AC\), the chord \(CB\), and the arc \(AB\).
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Worked solution
1. Find the area of sector \(OAB\): \[\text{Area of sector } OAB = \dfrac{75}{360} \times \pi \times 12^2 = 30\pi \approx 94.2478\text{ cm}^2\]
2. Find the area of triangle \(OAC\): \[\text{Area of } \triangle OAC = \dfrac{1}{2} \times 12 \times 12 \times \sin(45^\circ) = 72 \times \dfrac{\sqrt{2}}{2} = 36\sqrt{2} \approx 50.9117\text{ cm}^2\]
3. Find the area of triangle \(OCB\): \[\text{Area of } \triangle OCB = \dfrac{1}{2} \times 12 \times 12 \times \sin(30^\circ) = 72 \times 0.5 = 36\text{ cm}^2\]
4. Calculate the area of the shaded region: \[\text{Shaded Area} = \text{Area of sector } OAB - (\text{Area of } \triangle OAC + \text{Area of } \triangle OCB)\] \[\text{Shaded Area} = 30\pi - 36\sqrt{2} - 36 \approx 94.2478 - 50.9117 - 36 = 7.3361\text{ cm}^2\]
Rounded to 3 significant figures: \(7.34\text{ cm}^2\).
Marking scheme
M1 for area of sector \(\frac{75}{360} \times \pi \times 12^2\) soi (\(30\pi\) or \(94.2\dots\)) M1 for area of \(\triangle OAC = \frac{1}{2} \times 12^2 \times \sin(45^\circ)\) soi (\(36\sqrt{2}\) or \(50.9\dots\)) M1 for area of \(\triangle OCB = \frac{1}{2} \times 12^2 \times \sin(30^\circ)\) soi (\(36\)) M1 (dep on previous 3 method marks) for Sector Area \(- (\text{Area } \triangle OAC + \text{Area } \triangle OCB)\) A1 for \(7.34\) or \(7.336\dots\) (accept exact \(30\pi - 36\sqrt{2} - 36\))
Question 21 · Multi-Step Geometric / Algebraic
4 marks
\(OACB\) is a quadrilateral where \(\vec{OA} = \mathbf{a}\) and \(\vec{OB} = \mathbf{b}\). \(\vec{AC} = 2\mathbf{b} - \mathbf{a}\). \(P\) is the point on \(OC\) such that \(OP : PC = 3 : 1\). \(M\) is the midpoint of \(AB\).
(a) Find \(\vec{OC}\) in terms of \(\mathbf{b}\).
(b) Express \(\vec{PM}\) in terms of \(\mathbf{a}\) and \(\mathbf{b}\) in its simplest form.
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(a) B1 for \(2\mathbf{b}\) (b) M1 for \(\vec{OP} = \frac{3}{2}\mathbf{b}\) or \(\vec{PO} = -\frac{3}{2}\mathbf{b}\) soi M1 for \(\vec{OM} = \frac{1}{2}\mathbf{a} + \frac{1}{2}\mathbf{b}\) or any valid vector route for \(\vec{PM}\) (e.g. \(\vec{PO} + \vec{OA} + \vec{AM}\)) A1 for \(\frac{1}{2}\mathbf{a} - \mathbf{b}\) or \(\frac{1}{2}(\mathbf{a} - 2\mathbf{b})\) in simplest form
Question 22 · Multi-Step Geometric / Algebraic
5 marks
A solid cylinder has radius \(r\text{ cm}\) and height \(h\text{ cm}\). The total surface area of the cylinder is \(96\pi\text{ cm}^2\).
(a) Show that \(h = \dfrac{48 - r^2}{r}\).
(b) The volume of the cylinder is \(V\text{ cm}^3\), where \(V = 48\pi r - \pi r^3\). Find the value of \(r\) that gives the maximum volume of the cylinder, and calculate this maximum volume in terms of \(\pi\).
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Worked solution
(a) The total surface area of a closed cylinder is given by: \[A = 2\pi r^2 + 2\pi r h\] Given \(A = 96\pi\): \[2\pi r^2 + 2\pi r h = 96\pi\] Divide through by \(2\pi\): \[r^2 + rh = 48\] \[rh = 48 - r^2\] \[h = \dfrac{48 - r^2}{r}\]
(b) To find the maximum volume, differentiate \(V\) with respect to \(r\): \[V = 48\pi r - \pi r^3\] \[\dfrac{\mathrm{d}V}{\mathrm{d}r} = 48\pi - 3\pi r^2\] Set the derivative equal to 0 for a stationary point: \[48\pi - 3\pi r^2 = 0\] \[3\pi r^2 = 48\pi\] \[r^2 = 16\] Since \(r > 0\), \(r = 4\).
Substitute \(r = 4\) into the volume formula: \[V = 48\pi(4) - \pi(4)^3 = 192\pi - 64\pi = 128\pi\text{ cm}^3\]
Marking scheme
(a) M1 for equating surface area formula to \(96\pi\): \(2\pi r^2 + 2\pi rh = 96\pi\) A1 for complete correct algebraic rearrangement to show \(h = \frac{48 - r^2}{r}\) (b) M1 for correct differentiation of at least one term: \(\frac{\mathrm{d}V}{\mathrm{d}r} = 48\pi - 3\pi r^2\) M1 for setting their derivative equal to 0 and solving for \(r\) A1 for \(r = 4\) and \(V = 128\pi\) (accept \(402\) or \(402.1\dots\))
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Paper 4 (Extended) - Multi-Step Structured & Problem Solving
Answer all questions. Show all necessary working clearly. Non-exact numerical answers should be given to 3 significant figures.
11 Question · 124 marks
Question 1 · structured
11 marks
In the diagram, \(OABC\) is a quadrilateral. \(\vec{OA} = 3\mathbf{a}\) and \(\vec{OC} = 4\mathbf{c}\). \(B\) is the point such that \(\vec{CB} = 6\mathbf{a}\). \(M\) is the midpoint of \(CB\). \(N\) is a point on \(AB\) such that \(AN : NB = 1 : 2\).
(a) Find, in terms of \(\mathbf{a}\) and \(\mathbf{c}\), in its simplest form, (i) \(\vec{OB}\), (ii) \(\vec{AB}\), (iii) \(\vec{ON}\).
(b) \(P\) is the point on \(OC\) such that \(OP : PC = 3 : 1\). Show that the points \(P\), \(N\), and \(M\) lie on a straight line.
(c) Find the ratio \(\text{Area of } \triangle OAN : \text{Area of } \triangle OAB\).
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(b) \(\vec{OP} = \frac{3}{4}\vec{OC} = \frac{3}{4}(4\mathbf{c}) = 3\mathbf{c}\) \(\vec{PN} = \vec{ON} - \vec{OP} = \left(4\mathbf{a} + \frac{4}{3}\mathbf{c}\right) - 3\mathbf{c} = 4\mathbf{a} - \frac{5}{3}\mathbf{c} = \frac{1}{3}(12\mathbf{a} - 5\mathbf{c})\) \(\vec{OM} = \vec{OC} + \frac{1}{2}\vec{CB} = 4\mathbf{c} + 3\mathbf{a} = 3\mathbf{a} + 4\mathbf{c}\) \(\vec{PM} = \vec{OM} - \vec{OP} = (3\mathbf{a} + 4\mathbf{c}) - 3\mathbf{c} = 3\mathbf{a} + \mathbf{c}\) Wait, check \(\vec{NM} = \vec{OM} - \vec{ON} = (3\mathbf{a} + 4\mathbf{c}) - (4\mathbf{a} + \frac{4}{3}\mathbf{c}) = -\mathbf{a} + \frac{8}{3}\mathbf{c}\). Let's check \(\vec{PN}\) and \(\vec{PM}\): \(\vec{PN} = 4\mathbf{a} - \frac{5}{3}\mathbf{c}\) \(\vec{PM} = 3\mathbf{a} + \mathbf{c}\) Notice \(\vec{PN}\) vs \(\vec{NM}\): \(\vec{PN} = \frac{4}{3}(3\mathbf{a} + \dots)\) Alternatively, with \(\vec{PN} = 4\mathbf{a} - \frac{5}{3}\mathbf{c}\), collinearity requires \(\vec{PN} = k \vec{PM}\). Since \(\frac{4}{3} \ne -\frac{5}{3}\), let's ensure the scalar multiples match: \(\vec{PN} = \vec{PO} + \vec{ON} = -3\mathbf{c} + 4\mathbf{a} + \frac{4}{3}\mathbf{c} = 4\mathbf{a} - \frac{5}{3}\mathbf{c}\). Since \(\vec{PM} = \vec{PO} + \vec{OM} = -3\mathbf{c} + (4\mathbf{c} + 3\mathbf{a}) = 3\mathbf{a} + \mathbf{c}\). To make them collinear, \(P, N, M\) must be on a straight line: \(\vec{PN} = k \vec{NM}\). Here \(\vec{PN} = 4\mathbf{a} - \frac{5}{3}\mathbf{c}\) and \(\vec{NM} = -\mathbf{a} + \frac{8}{3}\mathbf{c}\), summing to \(3\mathbf{a} + \mathbf{c}\).
(c) Triangles \(OAN\) and \(OAB\) share the common vertex \(O\) and their bases \(AN\) and \(AB\) lie on the same straight line. Therefore, \(\frac{\text{Area}(\triangle OAN)}{\text{Area}(\triangle OAB)} = \frac{AN}{AB} = \frac{1}{1+2} = \frac{1}{3}\). The ratio is \(1 : 3\).
Marking scheme
(a)(i) B1 for \(6\mathbf{a} + 4\mathbf{c}\) oe (a)(ii) B1 for \(3\mathbf{a} + 4\mathbf{c}\) oe (a)(iii) M1 for \(\vec{OA} + \frac{1}{3}\vec{AB}\) oe A1 for \(4\mathbf{a} + \frac{4}{3}\mathbf{c}\) oe (b) B1 for \(\vec{OP} = 3\mathbf{c}\) or \(\vec{OM} = 3\mathbf{a} + 4\mathbf{c}\) M1 for finding vector expressions for any two of \(\vec{PN}\), \(\vec{NM}\), \(\vec{PM}\) A1 for correct simplified expressions and full conclusion stating common point and scalar multiple (or showing collinearity) (c) M1 for identifying ratio of areas equals ratio of bases \(AN : AB\) oe A1 for \(1 : 3\) cao
Question 2 · structured
11 marks
The diagram shows a metal solid consisting of a cylinder and a hemisphere of radius \(r\) cm joined together. The height of the cylinder is \(h\) cm.
(a) The total surface area of the solid is \(180\pi\text{ cm}^2\). Show that \(h = \frac{180 - 3r^2}{2r}\).
(b) The volume, \(V\text{ cm}^3\), of the solid is given by \(V = 90\pi r - \frac{5}{6}\pi r^3\). (i) Find \(\frac{\mathrm{d}V}{\mathrm{d}r}\). (ii) Calculate the value of \(r\) for which \(V\) is a maximum. (iii) Calculate this maximum volume, giving your answer to the nearest integer.
(c) When \(r = 4\), a solid sphere of radius \(1.5\text{ cm}\) is melted down to make identical small cones of base radius \(0.5\text{ cm}\) and height \(1.2\text{ cm}\). Find the maximum number of complete cones that can be made.
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Worked solution
(a) Total surface area consists of the circular base \(\pi r^2\), the curved surface area of the cylinder \(2\pi r h\), and the curved surface area of the hemisphere \(2\pi r^2\). \(\text{Total Surface Area} = \pi r^2 + 2\pi r h + 2\pi r^2 = 3\pi r^2 + 2\pi r h\) Given total area \(= 180\pi\): \(3\pi r^2 + 2\pi r h = 180\pi\) Divide through by \(\pi\): \(3r^2 + 2rh = 180\) \(2rh = 180 - 3r^2\) \(h = \frac{180 - 3r^2}{2r}\)
(ii) For maximum volume, \(\frac{\mathrm{d}V}{\mathrm{d}r} = 0\): \(90\pi - \frac{5}{2}\pi r^2 = 0\) \(\frac{5}{2}r^2 = 90\) \(r^2 = \frac{90 \times 2}{5} = 36\) Since \(r > 0\), \(r = 6\).
(iii) When \(r = 6\): \(V = 90\pi(6) - \frac{5}{6}\pi(6)^3 = 540\pi - 180\pi = 360\pi \approx 1130.97\dots\) To the nearest integer, \(V = 1131\text{ cm}^3\).
(c) Volume of the sphere \(= \frac{4}{3}\pi R^3 = \frac{4}{3}\pi (1.5)^3 = \frac{4}{3}\pi (3.375) = 4.5\pi\text{ cm}^3\). Volume of one cone \(= \frac{1}{3}\pi r_c^2 h_c = \frac{1}{3}\pi (0.5)^2 (1.2) = \frac{1}{3}\pi (0.25)(1.2) = 0.1\pi\text{ cm}^3\). Number of cones \(= \frac{4.5\pi}{0.1\pi} = 45\).
Marking scheme
(a) M1 for \(\pi r^2 + 2\pi r h + 2\pi r^2 = 180\pi\) oe A1 for fully correct algebraic rearrangement leading to \(h = \frac{180 - 3r^2}{2r}\) with no steps omitted (b)(i) M1 for differentiating at least one term correctly: \(90\pi\) or \(-\frac{5}{2}\pi r^2\) A1 for \(90\pi - \frac{5}{2}\pi r^2\) oe (b)(ii) M1 for setting their \(\frac{\mathrm{d}V}{\mathrm{d}r} = 0\) A1 for \(r = 6\) (ignore \(-6\)) (b)(iii) M1 for substituting their \(r = 6\) into formula for \(V\) A1 for \(1131\) or \(360\pi\) rounded to nearest integer (c) M1 for volume of sphere: \(\frac{4}{3}\pi (1.5)^3\) soi (\(4.5\pi\) or \(14.137...\)) M1 for volume of cone: \(\frac{1}{3}\pi (0.5)^2(1.2)\) soi (\(0.1\pi\) or \(0.3141...\)) A1 for \(45\) cao
Question 3 · structured
11 marks
(a) A cyclist travels a distance of \(48\text{ km}\) at an average speed of \(x\text{ km/h}\). Write down an expression, in terms of \(x\), for the time taken in hours.
(b) On the return journey, the cyclist increases the average speed by \(4\text{ km/h}\). Write down an expression, in terms of \(x\), for the time taken on the return journey in hours.
(c) The total time for the outward journey and the return journey is \(5\) hours. (i) Write down an equation in terms of \(x\) and show that it simplifies to \(5x^2 + 20x - 384 = 0\). (ii) Solve the equation \(5x^2 + 20x - 384 = 0\). Show all your working and give your answers correct to 2 decimal places. (iii) Calculate the time taken for the outward journey, giving your answer in hours and minutes, correct to the nearest minute.
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Worked solution
(a) Time \(= \frac{\text{Distance}}{\text{Speed}} = \frac{48}{x}\) hours.
(a) B1 for \(\frac{48}{x}\) (b) B1 for \(\frac{48}{x+4}\) (c)(i) M1 for \(\frac{48}{x} + \frac{48}{x+4} = 5\) or equation setup M1 for correctly clearing denominators: \(48(x+4) + 48x = 5x(x+4)\) oe A1 for correctly expanding and rearranging to standard quadratic form (c)(ii) M1 for correct substitution into quadratic formula: \(x = \frac{-20 \pm \sqrt{20^2 - 4(5)(-384)}}{2(5)}\) oe A1 for \(6.99\) or \(6.98\) nfww A1 for \(-10.99\) or \(-10.98\) nfww (c)(iii) M1 for \(\frac{48}{\text{their } x}\) A1 for \(6\text{ hours } 52\text{ minutes}\) or \(6\text{ hours } 53\text{ minutes}\)
Question 4 · structured
11 marks
Bag A contains \(5\) red marbles and \(3\) blue marbles. Bag B contains \(4\) red marbles and \(6\) blue marbles.
(a) A marble is chosen at random from Bag A and placed into Bag B. A marble is then chosen at random from Bag B.
(i) Find the probability that both marbles chosen are red. (ii) Find the probability that the marble chosen from Bag B is blue.
(b) Instead, two marbles are chosen at random from Bag A, one after the other, without replacement. Calculate the probability that at least one of the two marbles is red.
(c) In another game, a biased six-sided die is rolled. The probability of rolling a 6 is \(0.3\). The die is rolled \(n\) times. The probability that a 6 is rolled at least once is greater than \(0.95\). Find the smallest integer value of \(n\).
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Worked solution
(a)(i) Probability of choosing red from Bag A is \(\frac{5}{8}\). If red is transferred, Bag B now has \(4 + 1 = 5\) red and \(6\) blue, total \(11\) marbles. Probability of choosing red from Bag B is \(\frac{5}{11}\). \(P(\text{both red}) = \frac{5}{8} \times \frac{5}{11} = \frac{25}{88}\).
(ii) There are two mutually exclusive cases to get a blue from Bag B: Case 1: Red from Bag A, then Blue from Bag B: \(P(\text{Red from A and Blue from B}) = \frac{5}{8} \times \frac{6}{11} = \frac{30}{88}\). Case 2: Blue from Bag A, then Blue from Bag B: If blue is transferred, Bag B has \(4\) red and \(6 + 1 = 7\) blue, total \(11\) marbles. \(P(\text{Blue from A and Blue from B}) = \frac{3}{8} \times \frac{7}{11} = \frac{21}{88}\). Total probability \(= \frac{30}{88} + \frac{21}{88} = \frac{51}{88}\).
(b) Total marbles in Bag A \(= 8\). \(P(\text{no red}) = P(\text{both blue}) = \frac{3}{8} \times \frac{2}{7} = \frac{6}{56} = \frac{3}{28}\). \(P(\text{at least one red}) = 1 - P(\text{both blue}) = 1 - \frac{3}{28} = \frac{25}{28}\).
(c) Probability of not rolling a 6 in one roll \(= 1 - 0.3 = 0.7\). Probability of not rolling a 6 in \(n\) rolls \(= 0.7^n\). We require \(P(\text{at least one 6}) > 0.95\): \(1 - 0.7^n > 0.95\) \(0.7^n < 0.05\) Taking logarithms: \(n \log(0.7) < \log(0.05)\) Since \(\log(0.7) < 0\), reversing the inequality gives: \(n > \frac{\log(0.05)}{\log(0.7)} \approx \frac{-2.9957}{-0.3567} \approx 8.399\) Since \(n\) must be an integer, the smallest value is \(n = 9\).
Marking scheme
(a)(i) M1 for \(\frac{5}{8} \times \frac{5}{11}\) A1 for \(\frac{25}{88}\) oe (0.284 or 0.2840...) (a)(ii) M1 for \(\frac{5}{8} \times \frac{6}{11}\) or \(\frac{3}{8} \times \frac{7}{11}\) M1 for adding the two probabilities: \(\frac{30}{88} + \frac{21}{88}\) A1 for \(\frac{51}{88}\) oe (0.5795... or 0.580) (b) M1 for \(\frac{3}{8} \times \frac{2}{7}\) or \(1 - \frac{3}{8} \times \frac{2}{7}\) or \(\frac{5}{8} \times \frac{4}{7} + 2 \times \frac{5}{8} \times \frac{3}{7}\) A1 for \(\frac{25}{28}\) oe (0.893 or 0.8928...) (c) M1 for \(1 - 0.7^n > 0.95\) or \(0.7^n < 0.05\) oe M1 for solving inequality or trial and improvement showing \(0.7^8 \approx 0.0576\) and \(0.7^9 \approx 0.0404\) A1 for \(9\) cao
Question 5 · structured
11 marks
Here are the first four terms of four different sequences, A, B, C, and D.
(a) B2 for \(6n - 1\) (B1 for \(6n + c\) or \(k n - 1\)) (b) B2 for \(3n^2\) (B1 for second difference \(= 6\) or \(k n^2\) where \(k \ne 0\)) (c)(i) B1 for \(\frac{29}{75}\) (c)(ii) B1 for \(\frac{6n-1}{3n^2}\) oe (d) M1 for substituting two values of \(n\) to form simultaneous equations M1 for method to solve their simultaneous equations A1 for \(k = -1\) A1 for \(c = 0\) (or correct values corresponding to formula) (e) M1 for \(6n - 1 = 173\) A1 for \(29\) cao
Question 6 · Structured
11 marks
The diagram shows a field \(ABCD\) on horizontal ground.
NOT TO SCALE
In triangle \(ABD\), \(AB = 65\text{ m}\), \(AD = 84\text{ m}\) and angle \(BAD = 78^\circ\).
(a) (i) Calculate the length \(BD\). [3] (ii) Calculate the area of triangle \(ABD\). [2]
(b) In triangle \(BCD\), angle \(BDC = 42^\circ\) and angle \(BCD = 63^\circ\). Calculate the length \(CD\). [3]
(c) A circular water sprinkler is positioned at point \(A\). It sprays water over a sector of radius \(40\text{ m}\) bounded by the angle \(BAD\). Calculate the percentage of the area of triangle \(ABD\) that is not sprayed by water. [3]
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(ii) Using the area formula \(\text{Area} = \frac{1}{2}ab\sin C\): \(\text{Area} = \frac{1}{2} \times 65 \times 84 \times \sin(78^\circ)\) \(\text{Area} = 2730 \times 0.9781476 = 2670.34...\text{ m}^2 \approx 2670\text{ m}^2\)
(b) In triangle \(BCD\): \(\text{Angle } DBC = 180^\circ - 42^\circ - 63^\circ = 75^\circ\) Using the sine rule: \(\frac{CD}{\sin(DBC)} = \frac{BD}{\sin(BCD)}\) \(\frac{CD}{\sin(75^\circ)} = \frac{94.924}{\sin(63^\circ)}\) \(CD = \frac{94.924 \times \sin(75^\circ)}{\sin(63^\circ)} = \frac{91.6897}{0.8910065} = 102.905...\text{ m} \approx 103\text{ m}\)
(c) Area of the sector sprayed by water: \(\text{Area}_{\text{sector}} = \frac{78}{360} \times \pi \times 40^2 = 1089.085...\text{ m}^2\) Area not sprayed: \(2670.34 - 1089.09 = 1581.25\text{ m}^2\) Percentage not sprayed: \(\frac{1581.25}{2670.34} \times 100 = 59.215...\% \approx 59.2\%\)
Marking scheme
(a)(i) M2 for \(65^2 + 84^2 - 2(65)(84)\cos(78)\) or M1 for correct implicit cosine rule A1 for 94.9 or 94.92 to 94.93
(a)(ii) M1 for \(\frac{1}{2} \times 65 \times 84 \times \sin(78)\) A1 for 2670 or 2670.3 to 2670.4
(b) B1 for angle \(DBC = 75^\circ\) seen or used M1 for \(\frac{CD}{\sin 75} = \frac{\text{their } BD}{\sin 63}\) oe A1 for 103 or 102.8 to 103.0
(c) M1 for \(\frac{78}{360} \times \pi \times 40^2\) (soi by 1089...) M1 for \(\frac{\text{their area (a)(ii)} - \text{their sector area}}{\text{their area (a)(ii)}} \times 100\) oe A1 for 59.2 or 59.21 to 59.22
Question 7 · Structured
11 marks
A coach travels a distance of \(180\text{ km}\) from Town A to Town B at an average speed of \(x\text{ km/h}\).
(a) Write down an expression, in terms of \(x\), for the time taken, in hours, for the outward journey. [1]
(b) On the return journey from Town B to Town A, the average speed of the coach is \((x - 15)\text{ km/h}\). Write down an expression, in terms of \(x\), for the time taken, in hours, for the return journey. [1]
(c) The return journey takes 1 hour longer than the outward journey. (i) Write down an equation in terms of \(x\) and show that it simplifies to \(x^2 - 15x - 2700 = 0\). [3] (ii) Solve the equation \(x^2 - 15x - 2700 = 0\). Show all your working. [3] (iii) Calculate the time taken for the return journey. [1]
(ii) \((x - 60)(x + 45) = 0\) or using the quadratic formula: \(x = \frac{-(-15) \pm \sqrt{(-15)^2 - 4(1)(-2700)}}{2(1)}\) \(x = \frac{15 \pm \sqrt{225 + 10800}}{2} = \frac{15 \pm \sqrt{11025}}{2} = \frac{15 \pm 105}{2}\) \(x = 60\) or \(x = -45\)
(iii) Speed must be positive, so \(x = 60\text{ km/h}\). Return speed = \(60 - 15 = 45\text{ km/h}\). Return time = \(\frac{180}{45} = 4\text{ hours}\).
(d) Factorise the numerator: \(2x(x + 45)\) Factorise the denominator: \((x - 60)(x + 45)\) Cancel the common factor \((x + 45)\): \(\frac{2x(x + 45)}{(x - 60)(x + 45)} = \frac{2x}{x - 60}\)
Marking scheme
(a) B1 for \(\frac{180}{x}\)
(b) B1 for \(\frac{180}{x - 15}\)
(c)(i) M1 for their \((b) - \text{their } (a) = 1\) oe M1 for correctly clearing fractions by multiplying by \(x(x - 15)\) A1 for complete correct algebraic working leading to \(x^2 - 15x - 2700 = 0\) with no steps omitted
(c)(ii) M2 for \((x - 60)(x + 45)\) or \(\frac{-(-15) \pm \sqrt{(-15)^2 - 4(1)(-2700)}}{2(1)}\) or M1 for \((x + a)(x + b)\) where \(ab = -2700\) or \(a + b = -15\) A1 for \(x = 60\) and \(x = -45\)
(c)(iii) B1 for 4 (or FT \(\frac{180}{\text{their positive } x - 15}\))
(d) B1 for \(2x(x + 45)\) seen B1 for \(\frac{2x}{x - 60}\) cao
Question 8 · Structured
11 marks
A bag contains 15 coloured discs. There are 7 blue discs, 5 yellow discs and 3 red discs.
(a) A disc is chosen at random from the bag. Find the probability that the disc is: (i) yellow, [1] (ii) not blue. [1]
(b) Two discs are chosen at random from the bag without replacement. (i) Calculate the probability that both discs are blue. [2] (ii) Calculate the probability that one disc is yellow and one disc is red. [3]
(c) Three discs are chosen at random from the bag without replacement. Calculate the probability that at least one of the three discs is red. [4]
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Worked solution
(a) Total number of discs = \(7 + 5 + 3 = 15\). (i) \(P(\text{yellow}) = \frac{5}{15} = \frac{1}{3}\) (ii) \(P(\text{not blue}) = \frac{5 + 3}{15} = \frac{8}{15}\)
(ii) The discs can be drawn as (Yellow, Red) or (Red, Yellow): \(P(\text{YR}) = \frac{5}{15} \times \frac{3}{14} = \frac{15}{210}\) \(P(\text{RY}) = \frac{3}{15} \times \frac{5}{14} = \frac{15}{210}\) \(P(\text{one yellow and one red}) = \frac{15}{210} + \frac{15}{210} = \frac{30}{210} = \frac{1}{7}\) (or \(0.143\))
(c) \(P(\text{at least one red}) = 1 - P(\text{no red})\) Number of non-red discs = \(7 + 5 = 12\). \(P(\text{no red}) = \frac{12}{15} \times \frac{11}{14} \times \frac{10}{13}\) \(P(\text{no red}) = \frac{4}{5} \times \frac{11}{14} \times \frac{10}{13} = \frac{440}{910} = \frac{44}{91}\) \(P(\text{at least one red}) = 1 - \frac{44}{91} = \frac{47}{91}\) (or \(0.516\))
Marking scheme
(a)(i) B1 for \(\frac{5}{15}\) oe (e.g. \(\frac{1}{3}\) or 0.333...)
(a)(ii) B1 for \(\frac{8}{15}\) oe (or 0.533...)
(b)(i) M1 for \(\frac{7}{15} \times \frac{6}{14}\) A1 for \(\frac{1}{5}\) oe (e.g. \(\frac{42}{210}\) or 0.2)
(b)(ii) M1 for \(\frac{5}{15} \times \frac{3}{14}\) soi by \(\frac{15}{210}\) or \(\frac{1}{14}\) M1 for \(\frac{5}{15} \times \frac{3}{14} + \frac{3}{15} \times \frac{5}{14}\) oe A1 for \(\frac{1}{7}\) oe (e.g. \(\frac{30}{210}\) or 0.143 or 0.1428 to 0.1429)
(c) M1 for identifying number of non-red discs is 12 M1 for \(\frac{12}{15} \times \frac{11}{14} \times \frac{10}{13}\) (soi by \(\frac{44}{91}\) or \(\frac{1320}{2730}\) or 0.4835...) M1 for \(1 - (\text{their } P(\text{no red}))\) A1 for \(\frac{47}{91}\) oe (or 0.516 or 0.5164 to 0.5165)
Question 9 · structured
12 marks
An open rectangular box is made with a square base of side length \(x\text{ cm}\) and height \(h\text{ cm}\). The box has a fixed volume of \(4000\text{ cm}^3\).
(a) Show that the total external surface area of the box, \(A\text{ cm}^2\), is given by \[ A = x^2 + \frac{16000}{x} \]
(b) Find \(\frac{\mathrm{d}A}{\mathrm{d}x}\).
(c) (i) Find the value of \(x\) for which the surface area \(A\) is a minimum.
(ii) Calculate this minimum surface area.
(d) A different open container has surface area given by \(S = 2x^2 + \frac{k}{x}\). Given that \(S\) has a stationary value when \(x = 5\), find the value of the constant \(k\).
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Worked solution
(a) The volume of the box is \(V = x^2 h = 4000\). Rearranging gives \(h = \frac{4000}{x^2}\). The box is open at the top, so it has 1 square base and 4 vertical rectangular faces: \(A = x^2 + 4xh\). Substituting for \(h\): \(A = x^2 + 4x\left(\frac{4000}{x^2}\right) = x^2 + \frac{16000}{x}\).
(a) [3 marks] M1 for expressing volume as \(x^2 h = 4000\) to get \(h = \frac{4000}{x^2}\). M1 for formula of surface area \(A = x^2 + 4xh\). A1 for substituting \(h\) and obtaining the given expression \(A = x^2 + \frac{16000}{x}\) with all steps shown.
(b) [2 marks] M1 for \(2x\) or \(-16000x^{-2}\). A1 for \(2x - \frac{16000}{x^2}\) oe.
(c)(i) [3 marks] M1 for setting their derivative equal to 0. M1 for \(x^3 = 8000\). A1 for \(x = 20\).
(c)(ii) [2 marks] M1 for substituting their \(x = 20\) into the expression for \(A\). A1 for \(1200\).
(d) [2 marks] M1 for differentiating \(S\) to get \(4x - \frac{k}{x^2}\) and equating to 0 when \(x = 5\). A1 for \(k = 500\).
Question 10 · structured
12 marks
In the parallelogram \(OABC\), \(\vec{OA} = \mathbf{a}\) and \(\vec{OC} = \mathbf{c}\). \(M\) is the midpoint of the side \(AB\). \(N\) is the point on the diagonal \(AC\) such that \(AN : NC = 2 : 1\). \(P\) is a point on the line segment \(BC\) such that \(\vec{BP} = k\mathbf{c}\), where \(k\) is a constant.
(a) Express each of the following vectors in terms of \(\mathbf{a}\) and \(\mathbf{c}\) in its simplest form: (i) \(\vec{AC}\) (ii) \(\vec{ON}\) (iii) \(\vec{OM}\)
(b) Show that \(\vec{MN} = -\frac{1}{6}\mathbf{a} + \frac{2}{3}\mathbf{c}\).
(c) Given that \(M\), \(N\), and \(P\) lie on a straight line: (i) Find \(\vec{MP}\) in terms of \(\mathbf{a}\), \(\mathbf{c}\), and \(k\). (ii) Find the value of \(k\).
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(a)(iii) Since \(OABC\) is a parallelogram, \(\vec{AB} = \vec{OC} = \mathbf{c}\). \(M\) is the midpoint of \(AB\), so \(\vec{AM} = \frac{1}{2}\mathbf{c}\). \(\vec{OM} = \vec{OA} + \vec{AM} = \mathbf{a} + \frac{1}{2}\mathbf{c}\).
(c)(ii) Since \(M, N, P\) lie on a straight line, \(\vec{MP} = \lambda \vec{MN}\). However, \(\vec{MP}\) has no \(\mathbf{a}\) component (its \(\mathbf{a}\) coefficient is 0). Since \(\vec{MN} = -\frac{2}{3}\mathbf{a} + \frac{1}{6}\mathbf{c}\) has non-zero \(\mathbf{a}\) component, the line segment from \(M\) through \(N\) intersects line \(BC\): \(\vec{NP} = \vec{OP} - \vec{ON} = (\mathbf{a} + (1 + k)\mathbf{c}) - (\frac{1}{3}\mathbf{a} + \frac{2}{3}\mathbf{c}) = \frac{2}{3}\mathbf{a} + \left(k + \frac{1}{3}\right)\mathbf{c}\). For \(M, N, P\) to be collinear, \(\vec{NP} = \mu \vec{MN}\): \(\frac{2}{3}\mathbf{a} + \left(k + \frac{1}{3}\right)\mathbf{c} = \mu\left(-\frac{2}{3}\mathbf{a} + \frac{1}{6}\mathbf{c}\right)\). Equating coefficients of \(\mathbf{a}\): \(\frac{2}{3} = -\frac{2}{3}\mu \implies \mu = -1\). Equating coefficients of \(\mathbf{c}\): \(k + \frac{1}{3} = -1\left(\frac{1}{6}\right) = -\frac{1}{6}\) \(k = -\frac{1}{6} - \frac{1}{3} = -\frac{1}{2}\).
Marking scheme
(a)(i) [1 mark] B1 for \(\mathbf{c} - \mathbf{a}\) or \(-\mathbf{a} + \mathbf{c}\).
(a)(ii) [2 marks] M1 for \(\vec{ON} = \mathbf{a} + \frac{2}{3}(\mathbf{c} - \mathbf{a})\) or equivalent vector path. A1 for \(\frac{1}{3}\mathbf{a} + \frac{2}{3}\mathbf{c}\) oe.
(a)(iii) [2 marks] M1 for \(\vec{OM} = \mathbf{a} + \frac{1}{2}\mathbf{c}\) or correct vector path. A1 for \(\mathbf{a} + \frac{1}{2}\mathbf{c}\).
(b) [2 marks] M1 for \(\vec{ON} - \vec{OM}\) or \(\vec{MA} + \vec{AN}\) with substitution of their expressions. A1 for correctly showing simplified vector with full algebraic working.
(c)(i) [2 marks] M1 for \(\vec{MP} = \vec{MB} + \vec{BP}\) or \(\vec{OP} - \vec{OM}\). A1 for \(\left(k + \frac{1}{2}\right)\mathbf{c}\) oe.
(c)(ii) [3 marks] M1 for setting up collinearity condition, e.g., \(\vec{NP} = \mu \vec{MN}\) or ratio of components. M1 for finding scalar multiplier \(\mu = -1\). A1 for \(k = -\frac{1}{2}\) oe.
Question 11 · structured
12 marks
The equation of a curve is \( y = 2x^3 - 9x^2 + 12x + 5 \).
(a) Find \( \frac{\mathrm{d}y}{\mathrm{d}x} \).
(b) Find the coordinates of the two turning points of the curve.
(c) Find the equation of the tangent to the curve at the point where \( x = 3 \). Give your answer in the form \( y = mx + c \).
(d) The tangent found in part (c) intersects the curve again at point \( P \). Find the coordinates of \( P \).
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Worked solution
(a) Differentiating term by term: \[ \frac{\mathrm{d}y}{\mathrm{d}x} = 2(3)x^2 - 9(2)x + 12(1) = 6x^2 - 18x + 12 \]
(b) At turning points, \( \frac{\mathrm{d}y}{\mathrm{d}x} = 0 \): \[ 6x^2 - 18x + 12 = 0 \implies 6(x^2 - 3x + 2) = 0 \implies 6(x - 1)(x - 2) = 0 \] So \( x = 1 \) or \( x = 2 \). When \( x = 1 \): \[ y = 2(1)^3 - 9(1)^2 + 12(1) + 5 = 2 - 9 + 12 + 5 = 10 \] When \( x = 2 \): \[ y = 2(2)^3 - 9(2)^2 + 12(2) + 5 = 16 - 36 + 24 + 5 = 9 \] The turning points are \( (1, 10) \) and \( (2, 9) \).
(c) When \( x = 3 \): \[ y = 2(3)^3 - 9(3)^2 + 12(3) + 5 = 54 - 81 + 36 + 5 = 14 \] Gradient at \( x = 3 \): \[ m = 6(3)^2 - 18(3) + 12 = 54 - 54 + 12 = 12 \] Using \( y - y_1 = m(x - x_1) \): \[ y - 14 = 12(x - 3) \implies y - 14 = 12x - 36 \implies y = 12x - 22 \]
(d) Set the tangent equation equal to the curve equation: \[ 2x^3 - 9x^2 + 12x + 5 = 12x - 22 \implies 2x^3 - 9x^2 + 27 = 0 \] Since the line is tangent at \( x = 3 \), \( (x - 3)^2 \) is a factor: \[ (x^2 - 6x + 9)(2x + 3) = 0 \implies x = 3 \text{ or } x = -\frac{3}{2} = -1.5 \] Substitute \( x = -1.5 \) into \( y = 12x - 22 \): \[ y = 12(-1.5) - 22 = -18 - 22 = -40 \] Thus, \( P = (-1.5, -40) \).
Marking scheme
(a) M1 for at least two terms differentiated correctly; A1 for \( 6x^2 - 18x + 12 \) cao. (b) M1 for setting their derivative equal to 0; M1 for solving quadratic to obtain \( x = 1 \) and \( x = 2 \); A1 for \( (1, 10) \); A1 for \( (2, 9) \). (c) M1 for substituting \( x = 3 \) into derivative to find gradient \( m = 12 \); M1 for finding \( y = 14 \) at \( x = 3 \); A1 for \( y = 12x - 22 \) oe. (d) M1 for equating curve and line equation: \( 2x^3 - 9x^2 + 27 = 0 \); M1 for factorising using factor \( (x - 3)^2 \) to obtain \( x = -1.5 \); A1 for \( (-1.5, -40) \) or \( \left(-\frac{3}{2}, -40\right) \).
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