Question 456040
A hose can fill a children's pool in 3 hours. If the drain is open, the pool will drain in 5 hours. If the hose is turned on AND the drain is left open, how long will it take to fill the children's pool? 

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fill rate = 1/3 job/hr
drain rate = 1/5 job/hr
together rate = 1/x job/hr
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Equation:
fill - drain = 1 job
1/3 - 1/5 = 1/x
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5x - 3x = 15
2x = 15
x = 7.5 hrs. (time to fill the pool)
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Cheers,
Stan H.
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