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    Question

    There are two pipes to fill a tank. Together, they can

    fill the tank in 15 minutes. If one pipe can fill the tank in one and a half times as fast as the other, the faster pipe alone can fill the tank in:
    A 10 minutes Correct Answer Incorrect Answer
    B 25 minutes Correct Answer Incorrect Answer
    C 20 minutes Correct Answer Incorrect Answer
    D 32(1/2) Correct Answer Incorrect Answer

    Solution

    Let the slower pipe fill the tank in x minutes.  The faster pipe fills it in 2x/3 minutes (since it's 1.5 times faster). Their combined rate is: 1/x + 3/2x = 1/15 ⟹ 5/2x = 1/15 ⟹ x = 37.5 mins (slower pipe) The faster pipe takes: 2/3 x 37.5 = 25 mins

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