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Discussion :: Boats and Streams

  1. A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

    2. A.

    4
    B.

    5
    C.

    6
    D.

    10

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    Workspace

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    Answer : Option B

    Explanation :

    Let the speed of the stream be x km/hr. Then,

    Speed downstream = (15 + x) km/hr,

    Speed upstream = (15 - x) km/hr.

    \(\frac { 30 } { (15+X) }\)+\(\frac { 30 } { (15-X) }\)=4\( \frac { 1 } { 2 } \)

    \(\frac { 900} { 225 -X^2} \)=\( \frac { 9 } { 2 } \)

     9x2 = 225

     x2 = 25

     x = 5 km/hr.

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