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

    Question

    Speed of a boat in still water is 18 km/h while the

    speed of stream is ____ km/h. Total time taken by the boat to go 90 km upstream and 210 km downstream is ____ hours. The values given in which of the following options will fill the blanks in the same order in which it is given to make the above statement true: I. 7, 20 II. 5, 15 III. 9, 22.5 IV. 3, 18
    A Only I Correct Answer Incorrect Answer
    B Only II and IV Correct Answer Incorrect Answer
    C Only II and I Correct Answer Incorrect Answer
    D Only IV Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    For I: Speed of boat = 18 km/h Speed of stream = 7 km/h Speed in upstream = 18 – 7 = 11 km/h Speed in downstream = 18 + 7 = 25 km/h Total time = 90/11 + 210/25 = 8.18 + 8.4 = 16.58 hours So, I can’t be the answer. For II: Speed of boat = 18 km/h Speed of stream = 5 km/h Speed in upstream = 18 – 5 = 13 km/h Speed in downstream = 18 + 5 = 23 km/h Total time = 90/13 + 210/23 = 6.92 + 9.13 = 16.05 hours So, II can’t be the answer. For III: Speed of boat = 18 km/h Speed of stream = 9 km/h Speed in upstream = 18 – 9 = 9 km/h Speed in downstream = 18 + 9 = 27 km/h Total time = 90/9 + 210/27 = 10 + 7.78 = 17.78 hours So, III can’t be the answer. For IV: Speed of boat = 18 km/h Speed of stream = 3 km/h Speed in upstream = 18 – 3 = 15 km/h Speed in downstream = 18 + 3 = 21 km/h Total time = 90/15 + 210/21 = 6 + 10 = 16 hours So, IV can be the answer.

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