New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    An elephant can do a work as fast as two horses ‘A’

    and ‘B’ can do it by working together. If horse ‘A’ alone can complete the work in 20 hours and horse ‘B’ in 30 hours, then find the time taken by elephant to complete the work.
    A 12 hours Correct Answer Incorrect Answer
    B 10 hours Correct Answer Incorrect Answer
    C 18 hours Correct Answer Incorrect Answer
    D 24 hours Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the total work = 60 units Efficiency of horse who can complete the work in 20 hours = 60/20 = 3 units/hour Efficiency of horse who can complete the work in 30 hours = 60/30 = 2 units/hour Therefore, time taken by both horses to complete the work together = 60/(3 + 2) = 12 hours Therefore, time taken by the elephant to complete the work = 12 hours

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