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Question

Pipe ‘A’ can fill 25% of a tank in 6 hours while pipe ‘B’ takes 40 hours to empty fully filled tank. Pipe ‘A’ is opened alone when the tank was empty. After 12 hours, pipe ‘B’ is also opened. In how much time the tank will get filled this way?

A 24 hours Correct Answer Incorrect Answer
B 14 hours Correct Answer Incorrect Answer
C 4 hours Correct Answer Incorrect Answer
D 42 hours Correct Answer Incorrect Answer
E None of these Correct Answer Incorrect Answer

Solution

Time taken by pipe ‘A’ to fill the tank = 6/0.25 = 24 hours
Let, the total capacity of the tank be 120 units
Efficiency of pipe ‘A’ = 120/24 = 5 units/hour
Efficiency of pipe ‘B’ = 120/40 = 3 units/hour
Tank filled in 12 hours = 12 × 3 = 36 units
Time taken by pipe ‘A’ and pipe ‘B’ to fill the remaining tank = (120 – 36)/(5 – 3) = 30 hours
Therefore, total time taken = 12 + 30 = 42 hours

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