Rickety Bridge
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:1min,2mins,7mins and 10mins.
What is the shortest time needed for all four of them to cross the bridge? (NOTE: If it is 20 mins type 20)
The answer is 17.
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17 mins
(i) 1 and 2 go across = 2 mins (ii) 2 comes back = 2 mins (iii) 7 and 10 go across = 10mins (iv) 1 comes back = 1 min (v) 1 and 2 go across = 2 mins That's all! Total time = 17 mins