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    Question

    Pipes P, Q, and R can fill a tank in 15 hours, 10 hours,

    and 30 hours respectively. If the efficiencies of pipes P and Q are each reduced by 40% of their original efficiency and all three are opened together, find the total time taken by them to fill the tank.
    A 10 hrs Correct Answer Incorrect Answer
    B 5.4 hrs Correct Answer Incorrect Answer
    C 12 hrs Correct Answer Incorrect Answer
    D 7.5 hrs Correct Answer Incorrect Answer

    Solution

    ATQ, Let the capacity of the tank (LCM of 15, 10, and 30) be 30 liters. Efficiency of pipe P = 30/15 = 2 liters/hour Efficiency of pipe Q = 30/10 = 3 liters/hour Efficiency of pipe R = 30/30 = 1 liter/hour New efficiency of pipe P = 2 × (60/100) = 1.2 liters/hour New efficiency of pipe Q = 3 × (60/100) = 1.8 liters/hour Total efficiency = 1.2 + 1.8 + 1 = 4 liters/hour Required time = 30 / 4 = 7.5 hours

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