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Question 566089: One dran can empty pool in 20 hours, another in 25. If both drains work, how long to empty pool?
Answer by ptaylor(2198)   (Show Source):
You can put this solution on YOUR website! Let x=time required for both drains working together to drain the pool
Then both drains working together drains at the rate of 1/x pool per hour
One drain drains at the rate of 1/20 pool per hour
Another drains at the rate of 1/25 pool per hour
Together they drain at the rate of 1/20 + 1/25 pool per hour, soooo
1/20+1/25=1/x multiply each term by 100x
5x+4x=100
9x=100
x=11.11 hours
CK
In 11.11 hours one drains drains 11.11/20 of the pool
The other drains 11.11/25 of the pool
11.11/20 + 11.11/25 needs to equal 1 (1 pool, that is)
55.55/100 + 44.44/100=99.99/100 Close enough
Hope this helps---ptaylor
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