Crossing the Bridge (Math Riddle)
Fri, May 2, 2008
Four friends need to cross a bridge.
They start on the same side of the bridge.
A maximum of two people can cross at any time.
It is night and they have just one lamp.
People that cross the bridge must carry the lamp to see the way.
A pair must walk together at the rate of the slower person:
- Rachel: - takes 1 minute to cross
- Ben: - takes 2 minutes to cross
- George: - takes 7 minutes to cross
- Yvonne: - takes 10 minutes to cross
The second fastest solution gets the friends across in 21
minutes.
minutes.
The fastest takes 17 minutes. Can you work out how it is done?
Try your hand at this riddle using NRich’s interactive flash demo.
(Via NRich.)
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