Answer to question #25

25. Adam, Bob, Clair and Dave are out walking: They come to rickety old wooden bridge. The bridge is weak and only able to carry the weight of two of them at a time. Because they are in a rush and the light is fading they must cross in the minimum time possible and must carry a torch (flashlight,) on each crossing.
    
    They only have one torch and it can't be thrown. Because of their different fitness levels and some minor injuries they can all cross at different speeds. Adam can cross in 1 minute, Bob in 2 minutes, Clair in 5 minutes and Dave in 10 minutes.
    
    Adam, the brains of the group thinks for a moment and declares that the crossing can be completed in 17 minutes. There is no trick. How is this done????

This puzzle was e-mailed to me throught this website. The problem is not difficult to slove per se, certainly when you read the answer it seems simple....

Initialy most people would tend to assume the the quickest way is to have Adam (1) carry the torch and do all the running. Thi however, is not the case, the quickest time is achieved by having Clair(5) and Dave(10) cross together.

For simplicity Adam, Bob, Clair and Dave will be know as (1), (2), (5) & (10) respectively

The moves are as follows:

Move	Time
(1) & (2) Cross with Torch	2
(1) Returns with Torch	1
(5) & (10) Cross with Torch	10
(2) Returns with Torch	2
(1) & (2) Cross with Torch	2
	17 minutes

Alternatively the second move can be (2) returning with the torch, the times are the same.

 

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