There are many variations of the problem of crossing a river with various constraints on who or what can't be left together or be in the boat together. A well-known example being the Fox, Chicken and Corn Puzzle. We found a rather unusual variation on this in a very old book, and would like to share it.
A scout leader and four scouts had to cross a river by canoe. The canoe would hold only two people, and the scout leader and Sam were the only ones who could handle the canoe. The scouts were an argumentative bunch; James could not be left with either Sam or Tim, and neither could Tim be left with Larry. And for reasons of superstition, Larry refused to be part of the first crossing.
How did all five cross the river without any fights breaking out?
- Sam and Tim cross the river, leaving the scout leader with James and Larry,
- Sam returns, leaving Tim on the far bank,
- Sam and the scout leader cross the river, leaving James and Larry behind, who do not fight,
- The scout leader returns, leaving Sam with Tim, who also do not fight,
- The scout leader crosses the river with James, leaving Larry on his own,
- Sam returns, and the scout leader supervises Tim and James,
- Finally Sam brings Larry across the river, completing the crossing.