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    Question

    From a point on circular track 20 km long P, Q and R

    started running in the same direction at the same time with speed of 4 km per hour, 2 km per hour, 10 km per hour respectively. At what time they will meet again on the starting point
    A 12 hours Correct Answer Incorrect Answer
    B 19 hours Correct Answer Incorrect Answer
    C 15 hours Correct Answer Incorrect Answer
    D 10 hours Correct Answer Incorrect Answer

    Solution

    Distance = 20 km Speed of A = 4 km per hour Speed of B = 2 km per hour Speed of C = 10 km per hour Time = Distance/speed Time taken by A = 20/4 hours = 5 hours Time taken by B = 20/2 hours = 10 hours Time taken by C = 20/10 hours = 2 hours The required time = LCM of 5, 10, 2 = 10 ∴ All three will meet again at starting point after 10 hours

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