Math Is Fun Forum

10. Four people must cross a rickety footbridge at night. Many planks are missing, and the bridge can hold only two people at a time (any more than two, and the bridge collapses). The travellers must use a flashlight to guide their steps; otherwise they’re sure to step through a missing space and fall to their death. There is only one flashlight. The four people each travel at different speeds. Adam can cross the bridge in one minute; Larry in two minutes; Edge takes five minutes; and the slowest person, Bono, needs ten minutes. The bridge is going to collapse in exactly 17 minutes. How can all four people cross the bridge?