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Question 292091: It takes Sal 5 hours to paint a house. It takes Tom 3 hours to paint the same house. How long will it take to paint the house if both of them work together?
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! It takes Sal 5 hours to paint a house. It takes Tom 3 hours to paint the same house. How long will it take to paint the house if both of them work together?
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If you add the hours, it's 8 hours. Doesn't seem right, unless they drink a lot of beer and watch TV.
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Use the reciprocals, then you can add them.
Sal does 1/5 of the house per hour.
Tom does 1/3 per hour.
Together, they do 1/5 + 1/3 per hour = 8/15
8/15 house per hour --> 15/8 hours per house.
15/8 is it, or 1.875 hours.
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There's a shortcut, product/sum
3*5/(3+5) = 15/8
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