This is a pond in the shape of a prism. it is completely full of water. colin uses a pump to empty the pond. the level goes down by 20cm in the first 30 minutes. work out how many minutes colin has to wait for the pond to completely empty.

Volume of the prism is given by:
V=(base area)*(height)
thus:
base area=1/2(a+b)*h
=1/2(1.4+0.6)*2
=2 m²

Thus the volume will be:
V=2*1
V=2 m³

Volume after 30 min:
V=2×(0.8)
V=1.6 m³

Rate of emptying the tank is:
(2-1.6)/30=1/ 75 m³/min
time taken to empty the tank:
time=volume/rate
time=2/(1/75)
=150 min