Carroll's Cats-and-Rats Trap
If 6 cats can kill 6 rats in 6 minutes, how many cats does it take to kill 100 rats in 50 minutes? Most people blurt out '100' — Lewis Carroll built this word problem specifically to catch that instinct.
Reveal the answer
Scaling by rate, not by rat-count: each cat kills a rat every 6 minutes, so in 50 minutes one cat manages about 8⅓ rats — meaning 12 cats are needed for 100 rats, not 100 cats. Carroll published it in 'A Tangled Tale' (serialized in The Monthly Packet, 1880-85) and cheekily noted the 'honest' answer could be 12, 13, or 14 depending on unstated assumptions about how the cats cooperate — the whole point being how much a tidy word problem smuggles in.
— Lewis Carroll, A Tangled Tale — Serialized in The Monthly Packet, 1880-1885; collected 1885
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