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    Question

    ST

    A motor-cycle covers 90 km with a speed of 45 km/hr.

    find the speed of the motor-cycle for the next 90 km journey so that the average speed of the whole journey will be 65 km/hr.
    A 117 km/hr Correct Answer Incorrect Answer
    B 150 km/hr Correct Answer Incorrect Answer
    C 120 km/hr Correct Answer Incorrect Answer
    D 88 km/hr Correct Answer Incorrect Answer
    E 90 km/hr Correct Answer Incorrect Answer

    Solution

    Average speed of whole journey = 65 km/hr Using the formula, average speed = 2xy/(x + y) ⇒ x = speed of first 90 km = 45 km/hr ⇒ 65 = 2 × (45 × y)/(45 + y) ⇒ 117 km/hr 

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