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Question 63777: A sewage treatment plant has two inlet pipes to its settling pond. One can fill the pond in 10 hours, the other in 12 hours. If the first pipe is open for 5 hours and then the second pipe is opened, how long will it take to fill the pond?
Answer by venugopalramana(3286)   (Show Source):
You can put this solution on YOUR website! A sewage treatment plant has two inlet pipes to its settling pond. One (A)can fill the pond in 10 hours,the other(B) in 12 hours. If the first pipe is open for 5 hours and then the second pipe is opened, how long will it take to fill the pond?
A CAN FILL IN 1 HR...........1/10 TANK
A CAN FILL IN 5 HRS ...........5/10=1/2 TANK
REMAINING TANK TO BE FILLED............1-1/2 = 1/2 TANK
B CAN FILL IN 1 HR..........1/12 TANK
A+B CAN FILL IN 1 HR.....(1/10)+(1/12) = 22/120=11/60 TANK
A+B NEED .......60/11 HRS .........TO FILL 1 TANK
A+B NEED .......60/(11*2)=30/11HRS....TO FILL REMAINING 1/2 TANK.
HENCE IT TAKES A FURTHER 30/11 HRS TO FILL THE TANK...OR...
TOTAL 5+30/11 = 85/11=7.73 HRS TO FILL THE TANK
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