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    Question

    A train covers a certain distance at a speed of 24 km/h

    and the next same distance with a speed of 42 km/h and the next same distance with a speed of 72 km/h. find the average speed?
    A 12.6 km/hr Correct Answer Incorrect Answer
    B 30 km/hr Correct Answer Incorrect Answer
    C 45 km/hr Correct Answer Incorrect Answer
    D 37.8 km/hr Correct Answer Incorrect Answer

    Solution

    Since the distance is same in all the conditions. Therefore, Average speed = 3xyz/(xy + yz + zx) Average speed = 3 x 24 x 42 x 72/(24 x 42 + 42 x 72 + 24 x 72) Average speed = 3 x 24 x 42 x 72/(1008 + 3024 + 1728) = 217728/5760 = 37.8 km/hr    

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