The bridge will collapse in 17 minutes! Four people need to cross the bridge before it collapses. It is a dark night and they have only one flashlight among them.

Only two people can cross at a time.

Alice takes one minute to cross.

Bob takes two minutes.

Carol takes five minutes

Dave takes 10 minutes to cross.

How can they all get across before the bridge collapses? Click below to see the answer.

The trick to this puzzle is to get the slowest members of the group to cross only once together, while the fastest members cross back and forth multiple times.

Alice and Bob cross first using up 2 minutes.

Alice comes back making it 3.

Carol and Dave cross together making it 13 minutes.

Then Bob crosses back, making it 15 minutes.

Finally, Alice and Bob cross together to make it a total of 17 minutes.

2 comments:

Anonymous
said...

What does the flashlight have to do with anything? I'm assuming any party cannot cross without the flashlight?

## 2 comments:

What does the flashlight have to do with anything? I'm assuming any party cannot cross without the flashlight?

Yes, because it's dark, you can't cross the bridge without the flashlight.

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