Abe, Bill, Chris and Donald are all on one side of a narrow and dangerous bridge that they need to cross. It is late at night and very dark so they require a flashlight to cross safely. They have only one flashlight and the bridge is only strong enough to support the weight of two people at once. Each of the four people walk at different speeds: Abe can cross the bridge in one minute, Bill can cross in two minutes, Chris can cross in five minutes, and Donald can cross in ten minutes. When two people are walking together sharing the flashlight they can walk at the slower person’s pace.
How quickly can Abe, Bill, Chris and Donald cross the bridge safely?
