Wolf, Goat, and Cabbage
A farmer must ferry a wolf, a goat, and a cabbage across a river in a boat holding only himself and one item. Left unattended together, the wolf eats the goat and the goat eats the cabbage. What is the minimum number of river crossings needed to get everything across safely?
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Source: From Alcuin of York, 'Propositiones ad Acuendos Juvenes' (c. 800). Statement written for AxiomIQ.