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Question

Pipe ‘A’ can fill 25% of a tank in 3 hours while pipe ‘B’ takes 30 hours to empty fully filled tank. Pipe ‘A’ is opened alone when the tank was empty. After 9 hours, pipe ‘B’ is also opened. In how much time the tank will get filled this way?

A 2 hours Correct Answer Incorrect Answer
B 14 hours Correct Answer Incorrect Answer
C 4 hours Correct Answer Incorrect Answer
D 8 hours Correct Answer Incorrect Answer
E None of these Correct Answer Incorrect Answer

Solution

Time taken by pipe ‘A’ to fill the tank = 3/0.25 = 12 hours Let, the total capacity of the tank be 60 units Efficiency of pipe ‘A’ = 60/12 = 5 units/hour Efficiency of pipe ‘B’ = 60/30 = 2 units/hour Tank filled in 9 hours = 9 × 5 = 45 units Time taken by pipe ‘A’ and pipe ‘B’ to fill the remaining tank = (60 – 45)/(5 – 2) = 5 hours Therefore, total time taken = 9 + 5 = 14 hours

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