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    Question

    Two pipes, D and E, can fill a cistern in 26 and 78

    hours, respectively, while working alone. If the two pipes are opened together, the time taken to fill the cistern is:
    A 18(1/4) hours Correct Answer Incorrect Answer
    B 19(1/4) hours Correct Answer Incorrect Answer
    C 19(1/2) hours Correct Answer Incorrect Answer
    D 18(1/3) hours Correct Answer Incorrect Answer

    Solution

    Two pipes, D and E, can fill a cistern in 26 and 78 hours, respectively, while working alone. LCM of 26 and 78 is 78 which can be assumed as the total work. Efficiency of D = 78/26 = 3 units/hour Efficiency of E = 78/78 = 1 unit/hour If the two pipes are opened together, the time taken to fill the cistern = 78/(3+1) = 78/4 = 19.5 = 19(1/2) hours

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