A conical vessel has base radius 10 cm and depth 21 cm. Find its capacity in litres. Take π = 22/7.

Volume = (1/3)π$r^{2}h=(1/3)\times (22/7)\times 100\times 21=(1/3)\times 6600=2200{\text{cm}}^3$, and $1000{\text{cm}}^3=1$ litre, so the vessel holds 2.2 litres. (Leaving out the 1/3 — the mistake a cone invites most often — gives 6.6 litres; 2200 is the volume in ${\text{cm}}^3$, not litres; 0.22 divides by 10000 instead of 1000.)