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    Question

    Two pipes A and B can fill a tank in 24 min., and 32

    min, respectively. If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 minutes?
    A 8 min Correct Answer Incorrect Answer
    B 16 min Correct Answer Incorrect Answer
    C 5 min Correct Answer Incorrect Answer
    D 13 min Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let B be closed after x minutes. Then, Part filled by (A+B) in x min. + part filled by A in (18 – x) min. = 1 x (1/24 + 1/32) + (18 – x ) × 1/24 = 1 ⟹ 7x/96 + (18 - x)/24 = 1 ⟹7 x + 4 (18 – x) = 96 ∴ x = 8 ∴ Hence, B must be closed after 8 minutes

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