Fifteen people are trapped aboard a ship that's going to sink in exactly 20 minutes. Their only chance of survival is the five-person life raft stowed on their vessel. To make matters worse, the waters around the ship are teeming with man eating sharks, so swimming to safety is out of the question. A round trip to the nearest island and back to the boat takes nine minutes on the raft. How many people will live to see dry land?
ps: for those who know the answer, please dont spoil it.