Four people need to cross an old bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without torch.
- 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 min, 2 mins, 7 mins and 10 mins respectively.
What is the shortest time needed for all four of them to cross the bridge?