Four people have to cross an old, rickety bridge over deep cold water infested w

Question

Four people have to cross an old, rickety bridge over deep cold water infested with sharks, alligators, crocodiles and shrieking eels. The bridge is so old that it can hold no more than two people at any one time.

It's the middle of the night, so on every trip across the bridge, the person crossing needs to use the group's only flashlight to cross safely.

The four people who need to cross the bridge all walk at different speeds. One person takes 1 minute to cross, one person takes 2 minutes, one takes 5 minutes, and one take 10 minutes. If two people cross together, they need to stay together to share the flashlight, and so they cross at the speed of the slower person.

For example, the 1-minute person can cross with the 10-minute person. This trip will take 10 minutes.

How quickly you can get all four people across the bridge.


(Please try to show your work and try to get past 19 minutes.)

Explanation / Answer

1 Minute and 2 Minute Cross = 2 Minutes 1 Minute goes back = 3 Minutes 5 Minute and 10 Minute Cross = 13 Minutes 2 Minute goes back = 15 Minutes 1 Minute and 2 Minute cross = 17 Minutes

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