4 men crossing a bridge
There are 4 men who want to cross a bridge. They all begin on the same side. You have 17 minutes to get all of them across to the other side. It is night. There is one flashlight. A maximum of two people can cross at one time.
Any party who crosses, either 1 or 2 people, must have the flashlight with them. The flashlight must be walked back and forth, it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the rate of the slower man's pace.
Man 1: 1 minute to cross
For example if Man 1 and Man 4 walk across first. 10 minutes have elapsed when they get to the other side of the bridge. If Man 4 returns with the flashlight. A total of 20 minutes have passed and you have failed the mission.