SOLUTION: Sally can clean the house in 4 hours, her father can clean the house in 2 hours, and her younger brother, Dennis, can completely mess up the house in 10 hours. If Sally and her fat

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Question 869467: Sally can clean the house in 4 hours, her father can clean the house in 2 hours, and her younger brother, Dennis, can completely mess up the house in 10 hours. If Sally and her father clean and Dennis plays, how long will it take to clean the house?

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Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
1/4+1/2-1/10=1/x
Every hour Dad cleans half the house
Every hour Sally cleans one quarter of the house
Every hour Dennis messes up 1/10 of the house.
x = 20/13
x = 1.5385 hours