There are 3 missionaries and 3 cannibals that need to cross a river. There is only 1 way across the river and that is by boat. There is only 1 boat and the boat will hold at most two people. You cannot have more cannibals than missionaries on one side of the river or else the cannibals will eat the missionaries and you fail. How do they all cross the river?
I will call the starting place side A and the destination side B.
1) Send 1 cannibal and 1 missionary across the river.
2) Drop off the cannibal at side B and send back the missionary to side A.
3) Drop off the missionary at side A and send over 2 cannibals to side B.
4) Drop 1 cannibal off at side B and then go back to side A.
5) Drop off the cannibal at Side A and send over 2 missionaries.
6) Drop 1 missionary off at side B, then pick up a cannibal from side B and go back to side A.
7) Drop off the cannibal at side A and pick up a missionary from Side.
8) Drop off both missionaries at side B and then send 1 cannibal from side B back.
9) Pick up a cannibal from side A and take him to side B.
10) Drop 1 cannibal off at side B and go back to side A.
11) Pick up the final cannibal from side A and take him over to side B.
12) Drop off both cannibals.