PROBLEM:
A man needs to cross a river in a canoe.  With him, he has a bag of grain, a chicken, and a fox.  He can only carry one of the three at a time.  If he leaves the grain and the chicken, the chicken will eat the grain.  If he takes the grain, the fox will eat the chicken.

How does he successfully cross the river with his load?
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SOLUTION: 
The man first takes the chicken across, leaving it on the other side.  He returns alone in the canoe and picks up the bag of grain.  After bringing across the grain, he takes the chicken back to the original side, dropping him off, and picking up the fox.  After bringing the fox to the other side, and leaving it with the grain, the man returns back to the original side, retrieving the chicken, and making his 3rd and final trip crossing the river.  At no point was the fox left alone with the chicken, or the chicken with the grain.