The Bridge

Dave 0

There is a bridge.

The bridge can only support 2 people at a time.

There are 4 people.

Each person takes a different amount of time to cross the bridge:

Person 1 = 1 minute

Person 2 = 2 minutes

Person 3 = 5 minutes

Person 4 = 10 minutes

 

It is dark, and there is only 1 flashlight. Thus, you need the flashlight to cross the bridge. That means people must travel in pairs.

What is the least amount of time it takes for all 4 people to cross?

Note: Nothing strange – you can’t throw the flashlight back across, you can’t ‘shine the light ahead’ for one of the people, etc. It’s simple.

 
 
 
 
ANSWER BELOW:
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The answer is 17 minutes.
 
1 and 2 cross, 1 comes back = 3 minutes this trip.
5 and 10 cross, 2 comes back = 12 minutes trip, 15 minutes total.
1 and 2 cross = 2 minutes this trip, 17 minutes total.