Exams › SSC CGL (Prelims) › General

Three pumps, A, B, and C, can fill a reservoir. A fills it in 5 hours, B in 7 hours, and C in 10 hours. When all three pumps are opened together, they operate for 1.5 hours before pump C is closed. How much additional time will it take to completely fill the reservoir after that?

1. 1/2 hours
2. 43/25 hours
3. 47/48 hours
4. 45/41 hours

Correct answer: 47/48 hours

Solution

Together, A, B, and C fill at a rate of 1/5 + 1/7 + 1/10 = 31/70 of the reservoir per hour. In 1.5 hours, they fill 93/140, leaving 47/140. After C is closed, A and B fill at 1/5 + 1/7 = 12/35 per hour, so the remaining time is (47/140) ÷ (12/35) = 47/48 hours.

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