Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge.
Times for each person: 1 minute, 2 minutes, 7 minutes and 10 minutes.
What is the shortest time needed for all four of them to cross the bridge?
