<PRE><B>Question 332663</B>
Put things in terms of proportion of the pool emptied or filled per hour
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Fiilled:  1/10 of the pool every hour
Emptied:  -1/19 of the pool every hour (negative means its being drained)
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filled if drain is open:  both fill and drain at the same time (working together)  =  1/10 - 1/19 every hour
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So every hour  1/10 - 1/19  fill 1/x of the pool
1/10-1/19=1/x
get common denominator
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19/190 - 10/190 = 1/x
9/190 = 1/x  (solve for x)
x=190/9= 21+1/9 hours or apprx 21 hours and 7 minutes



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