A volcano erupts in the dark of the night. Four people, carrying only one flashlight, run for their lives. They come to a canyon. There's a footbridge that spans the canyon. The bridge can only support 2 people at a time. Since it's dark, they must use a flashlight to cross. Therefore, after 2 people cross safely, one has to go back to bring the flashlight back to the other side.
The people, suffering from different injuries, travel across the bridge at different speeds. Person #1 takes 1 minute, person #2 takes 2 minutes, person #3 takes 5 minutes, and person #4 takes 10 minutes. Two people crossing the bridge will travel at the speed of the slower person. There are only 17 minutes before the lava destroys the bridge. Find a logical solution where all four people reach the other side safely in 17 minutes or less—but this solution cannot include having any of them go only halfway across, or go across in the dark, or throw the flashlight across, etc. AND REMEMBER: You also have to count the time it takes to go back across the bridge with the flashlight!