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Puzzle ZBWT 



?

Sam takes 20 days to build a wall.

Taylor and Kelly both take 10 days to build a wall.

How long will it take the three of them to build a wall if they work together?

Puzzle Copyright © Kevin Stone

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Answer
4 days.

Reasoning
In one day Sam can build 1/20 of a wall, Taylor and Kelly can each build 1/10.

So in one day, in total, they can build 1/20 + 1/10 + 1/10 = 1/4.

Therefore the wall will take 4 days to build.

 

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