An 8th century writer declared that every child over the age of 11 knew this puzzle. So you’ve probably heard of it too, but it remains one of the best ways of introducing the idea of logic.
Suppose a man is travelling with a wolf, a goat and some cabbages. He comes to a river with a boat that can only carry two at a time. Now if he travels across carrying the wolf and then comes back for the other two, the goat would have eaten the cabbages by the time he gets back. Similarly, if he travels across with the cabbages, the wolf would have killed the goat by the time he returns. So how can he get everything across intact?
Obviously, the first step has to be to take the goat across. This leaves the wolf with the cabbages and presumably they will leave each other alone till the man returns.
Wolf + Goat + cabbage + man <boat> Other side
Wolf + cabbage <man + goat>
Crossing 2 (Return)
Wolf + cabbage <man> Goat
He then takes the cabbages across leaving the wolf alone on the first side, but on the return trip, he brings the goat back with him leaving only the cabbages across the river.
Wolf <man+cabbage> Goat
Crossing 4 (Return)
Wolf <man+goat> cabbage
Now the man is with the wolf and goat on one side with the cabbages across. He then takes the wolf and crosses the river again and comes back alone. Note that now the wolf has been left with the cabbages a second time only this time it is across the river.
Goat <man+wolf> cabbage
Crossing 6 (Return)
Goat <man> cabbage + wolf
Finally, the man takes the goat across the river and can then proceed along his way.
<man + goat> cabbage + wolf
Wolf + Goat + cabbage + man
For the pedant, the BBC pointed out that wolves are opportunistic hunters and have been known to eat vegetation when required so the cabbage isn’t perfectly safe. Finally, what kind of man travels with a wolf?