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Puzzle ZBWT 



?

Sam takes 20 days to build a wall.

Taylor and Kelly each 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 20 days, Sam can build 1 wall, and Taylor and Kelly can each build 2 walls.

So, in 20 days, 5 walls can be built.

Therefore, one wall will take 4 days to build.

 

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