Question 621623
Two drains takes 9 hours each to completely remove the water from similar-sizes(same volume) pools. The first drain was opened at 6 a.m. Two hours after, the second drain is opened. At what time will the remaining volume in the second pool be three times the remaining volume in the first pool?
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1/9=work rate of both pools
let x=hours drain open for second pool
x+2=hours drain open for first pool
volume=work rate*hours drains are open
x/9=volume drained for second pool
(x+2)/9=volume drained for first  pool
..
((x+2)/9)/(x/9)=3
(x+2)/x=3
3x=x+2
2x=2
x=1 hr
Remaining volume in the second pool be three times the remaining volume in the first pool 3 hours after the first drain is open at 9 a.m.