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Pipes A, B and C can fill an empty tank in (30/7) hours if all the three pipes are opened simultaneously. A and B are filling pipes and C is an emptying pipe. Pipe A can fill the tank in 15 hours and pipe C can empty it in 12 hours. In how long (in hours) can pipe B alone fill the empty tank?1. 62. 33. 44. 5 |
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Answer» Correct Answer - Option 3 : 4 Given: Pipes A, B and C can fill an empty tank in 30/7 hours A and B are filling pipes and C is an emptying pipe. Time taken by A and B together to fill the tank = 15 hours Time taken by C to empty the tank alone = 12 hours Concept: Efficiency = 1/(Total time) Calculation: let time taken by B be X hr. Work done by B in 1 hr = 1/X hr. Work done by (A + B – C) in 1 hr = 7/30 According to the question: ⇒ (1/15) + (1/X) – (1/12) = 7/30 ⇒ 1/X = (7/30) + (1/12) – (1/15) ⇒ 1/X = (14 + 5 – 4)/60 ⇒ 1/X = 15/60 ⇒ 1/X = 1/4 ⇒ X = 4 ∴ Time taken by B is 4 hr. |
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