Four people need to cross a bridge at night. They have only one torch and the bridge is too dangerous to cross without one. The bridge is strong enough only to support two people at a time. Not all people take the same time to cross the bridge. Time for each person: 1 min, 2 mins, 7 mins, 10 mins. What is the minimum time needed for all four of them to cross the bridge?
Answer : 10 mins.
A and D crosses the bridge. D holds the torch.
In one minute A crosses the bridge.
B starts to cross the bridge. B finishes it two minutes.
C starts to cross the bridge. Takes 7 minutes to finish. Mean while, A also finishes crossing the bridge.
Minimum time need for all : 10 minutes.
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