Problem:

Three missionaries and three cannibals must cross a river using a boat that can carry up to two people. How can they all get to the other side without ever leaving a group of missionaries outnumbered by cannibals on either side of the river?

Scroll to the bottom of the page for the answer

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Solution:

The boat must never leave more cannibals than missionaries on either side. They start by taking two cannibals across, one cannibal returns, then two missionaries go over, one missionary and one cannibal return, the two remaining cannibals go over, one cannibal returns, and finally, the last two missionaries go over.