Question

    A motor boat covers a certain distance downstream in a

    river in 3 hours and 30 minutes. It covers the same distance upstream in 4 hours. If the speed of water is 3 km/h, then the speed of the boat in still water is:
    A 27 km/hr Correct Answer Incorrect Answer
    B 15 km/hr Correct Answer Incorrect Answer
    C 34 km/hr Correct Answer Incorrect Answer
    D 45 km/hr Correct Answer Incorrect Answer
    E 42 km/hr Correct Answer Incorrect Answer

    Solution

    Let the speed of boat in still water be x km/hr and the distance be y km. Rate downstream = (x + 3) km/hr Rate upstream = (x – 3) km/hr According to the question, y/(x + 3) = 7/2 --- (i) y/(x – 3) = 4 --- (ii) On dividing equation (i) by (ii), (x – 3)/(x + 3) = (7/2)/4 = 7/8 8x – 24 = 7x + 21 x = 21 + 24 = 45 kmph

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