Problem:

Four people need to cross a rickety bridge at night. They have one flashlight and can only cross two at a time, and they must walk at the pace of the slower person. Their walking speeds are 1, 2, 5, and 10 minutes. The bridge can only hold them for 17 minutes. How do they all cross in time?

Scroll to the bottom of the page for the answer

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Solution:

The two fastest (1 and 2 minutes) cross first, with the 1-minute person returning with the flashlight. Then, the two slowest (5 and 10 minutes) cross. The 2-minute person goes back, and the two fastest cross again.