EXTENSION: The canal was built in the 1890s. The depth of the cut down to the water level ranges from 20 m at each end to 80 m in the middle, with an average depth of 50 m. Use either scale drawing or ratios to work out the total volume of rock removed.

Diagnostic and formative information:

Common error

Likely calculation

Likely reason

a)

200
176

25 × 8
22 × 8

Calculates area of a rectangle rather than a trapesium.