A wooden block measuring 14 cm by 14 cm by 20 cm has a cylindrical hole of radius 3.5 cm bored straight through it, entering one 14 cm by 14 cm face and leaving through the opposite one. How much wood, in cubic cm, is left? (Use π = 22/7.)

The block is $14\times 14\times$ 20 = 3920 cubic cm. The bore is a cylinder of radius 3.5 cm and length 20 cm, holding (22/7) $\times 3.5^{2}x20=38.5\times 20=770$ cubic cm. The wood left = 3920 - 770 = 3150 cubic cm. The trap 3920 forgets to bore the hole at all; 770 reports the sawdust rather than the wood; 840 reads 3.5 cm as the hole's DIAMETER doubled to a radius of 7 cm, which removes 3080 cubic cm — four times too much.