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    Question

    A boat running downstream covers a distance of 36 km in

    3 hrs while it covers the same distance upstream in 4 hrs. Then speed of the boat in still water is
    A 12 km/hr Correct Answer Incorrect Answer
    B 9 km/hr Correct Answer Incorrect Answer
    C 6 km/hr Correct Answer Incorrect Answer
    D 18 km/hr Correct Answer Incorrect Answer
    E 10.5 km/hr Correct Answer Incorrect Answer

    Solution

    Let the speed of boat in still water be a km/hr and that of stream be b km/hr. Therefore, 36/(a + b)= 3 ⇒ a + b = 12 ………..(i) 36/(a – b)= 4 ⇒ a + b = 9 ………..(ii) On adding, eq (i) and (ii) ⇒ 2a = 21 km/hr ⇒ a = 10.5 km/hr

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