Question 142242
Joe cleans his room in 7 hours. With his mom, it takes them 3 hours. How long does it take mom alone?
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Joe's rate = 1/7 job/hr
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Joe and Mom together's rate = 1/3 job/hr.
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Mom's rate alone is 1/x job/hr
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EQUATION:
rate + rate = together rate
1/7 + 1/x = 1/3
Multiply thru by 21x to get:
3x + 21 = 7x
4x = 21
x = 21/4 = 5 1/4 hr (time it will take Mom alone)
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Cheers,
Stan H.