Last week’s math riddle was such a hit with our readers that we just can’t resist:

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:

Man 1: 1 minute to cross

Man 2: 2 minutes to cross

Man 3: 5 minutes to cross

Man 4: 10 minutes 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.

(H/T again to Professor Steve Miller of Williams College.)

And kudos to Ray Ward, who solved last week’s puzzle and posted the answer in a “comment.”