A solid block of lead measuring 66 cm by 42 cm by 21 cm is melted and cast into spherical bullets of diameter 4.2 cm. How many bullets are made? Take π = 22/7.

Block = $66\times 42\times 21=58212{\text{cm}}^3$. Each bullet has radius 2.1 cm, so its volume = $(4/3)\times (22/7)\times 2.1^3=(4/3)\times (22/7)\times 9.261=38.808{\text{cm}}^3$. Number = 58212/38.808 = 1500. (Dropping the 4/3 and using π$r^3$ gives 2000; treating a bullet as a hemisphere, (2/3)π$r^3$, gives 3000; using the cone formula (1/3)π$r^3$ gives 6000.)