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    Question

    Three pipes are attached to a tank. Pipe A can fill it

    in 20 minutes, pipe B can fill it in 30 minutes, while pipe C can empty the completely filled tank in 15 minutes. If pipe A is opened first, pipe B is opened 5 minutes after pipe A and pipe C is opened 10 minutes after pipe A, find the total time taken to fill the tank.
    A 18 min Correct Answer Incorrect Answer
    B 20 min Correct Answer Incorrect Answer
    C 22 min Correct Answer Incorrect Answer
    D 25 min Correct Answer Incorrect Answer
    E 30 min Correct Answer Incorrect Answer

    Solution

    Let the capacity of the tank be 60 litres . {LCM (20, 30 and 15)}
    So, efficiency of inlet pipe A = 60 ÷ 20 = 3 litres /minute
    And, efficiency of inlet pipe B = 60 ÷ 30 = 2 litres /minute
    And, efficiency of outlet pipe C = 60 ÷ 15 = 4 litres /minute
    In first 5 minutes , pipe A will fill 5 × 3 = 15 litres
    And, pipes A and B together will fill 5 × (3 + 2) = 25 litres
    So, required time = 5 + 5 + {(60 − 15 − 25) ÷ (3 + 2 − 4)} = 30 minutes

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