This may look like a simple math problem but if it were merely a division problem, it would not be much of a brainteaser. We are trained as young children to work out math problems in school. When I was young, I loved math but always dreaded the word problems. This puzzle is not a word problem in the traditional sense. This puzzle demands you take more time working through the steps and not just focusing on the division. You will quickly see that there is more to in than basic arithmetic.
If you visualize the life raft taking crew members off the boat and depositing them on the island it will quickly become clear that you should not count the crew member rowing the boat. An empty boat cannot make it back to the ship! Then there is the time limit. If you do basic division you could miss a boat trip. The life raft can still take crew members to safety even while the ship sinks fully. You then have to count the pilot of the raft as he will not be returning to the sunken ship.