Water runs along a canal 5 m wide and 2 m deep at 8 km per hour. For how many minutes must it run to irrigate 32 hectares of land to a standing depth of 10 cm? Take 1 hectare = $10000{\text{m}}^2$.

The land measures $32\times 10000=320000{\text{m}}^2$, and 10 cm = 0.1 m deep needs $320000\times 0.1=32000{\text{m}}^3$ of water. In one hour the canal delivers a block 5 m × 2 m × 8000 m = $80000{\text{m}}^3$. Time = 32000/80000 = 0.4 hour = 24 minutes. (Ignoring the canal's 2 m depth halves the supply and gives 48 minutes; reading 10 cm as 1 m gives 240 minutes; taking a hectare as $1000{\text{m}}^2$ gives 2.4 minutes.)