New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    A boat running downstream covers a distance of 42 km in

    2 hrs while it covers the same distance upstream in 7 hrs. Then speed of the boat in still water is
    A 21 km/hr Correct Answer Incorrect Answer
    B 27 km/hr Correct Answer Incorrect Answer
    C 6 km/hr Correct Answer Incorrect Answer
    D 13.5 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, 42/(a + b)= 2 ⇒ a + b = 21 ………..(i) 42/(a – b)= 7 ⇒ a + b = 6 ………..(ii) On adding, eq (i) and (ii) ⇒ 2a = 27 km/hr ⇒ a = 13.5 km/hr

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