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    Question

    Two pipes A and B can fill a tank in 4 hours and 7 hours

    respectively & a waste pipe C can empty in 8 hours. If pipes A , B & C are opened at 7am , 8am & 9am respectively, then at what time tank will be completely filled?
    A 8.20 am Correct Answer Incorrect Answer
    B 7.10 am Correct Answer Incorrect Answer
    C 10.20 am Correct Answer Incorrect Answer
    D 8.15 am Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    A can Fill a tank in 4 hours and B can do the same in 7 hours & C can empty tank in 8 hrs. Let Total Work = LCM (4, 7 & 8) = 56 units Work done in 1st hr by A = 14 units Work done in 2nd hr by A & B = 14+8 = 22 units; Total work done in 2 hrs = 22 + 14 = 36 units, Now pending work = 56 – 36 = 20 units Work done in 3rd hr = 14 + 8 – 7 = 15 units Remaining work = 20 - 15 = 5 units Time taken to complete the remaining work = 5/15 = 1/3 = 20 min Hence work will be completed at = 7am + 3.20 = 10.20 am.

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