The four operations：練習題

Evaluate the expression: \( (18 - 6) \div 3 + 4 \times 2 \).

A diver is \( 15.5 \) metres below sea level. They descend a further \( 4.2 \) metres and then ascend \( 8.7 \) metres. What is their final depth relative to sea level?

A metal plate has a mass of \( 3.45\text{ kg} \). Six identical holes are drilled into the plate. Each hole removes \( 12.5\text{ g} \) of metal. Calculate the remaining mass of the plate in grams.

Work out \( 15 - 3(2 + 4) \).

Evaluate \( \frac{-12 + (-3) \times 4}{2^2} \).

Evaluate \( 15 - ( -3 ) \times 6 \).

Evaluate the expression \( 4.5 \div (0.5)^2 - (-3.2 \times 2) \).

Evaluate the expression \( \frac{(-12 + 4 \times -3) \div (-2)^2 - \sqrt[3]{-1}}{0.5} \).

(a) Evaluate the expression: \( 24 \div ( -2 )^3 + 5 \times ( -4 ) \).
(b) At 06:00, the temperature in a city was \( -5^\circ\text{C} \). By 10:00, the temperature had risen by \( 12^\circ\text{C} \). By 14:00, it had fallen by \( 3^\circ\text{C} \) from the 10:00 reading. Calculate the temperature at 14:00.

A submarine is at a depth of 145.5 metres below sea level.
(a) The submarine ascends at a constant rate of 12.4 metres per minute. Calculate its depth below sea level after 6 minutes.
(b) From this new position, the submarine then descends a further \( 82 \frac{3}{4} \) metres. Calculate its final depth below sea level.
(c) A second submarine is located at a depth of 210.2 metres below sea level. Calculate the vertical distance between the final depth of the first submarine and the second submarine.