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1. A person can row $7 \frac{1}{2}$ km an hour in still water. Finds that it takes twice the time to row upstream than the time to row downstream. The speed of the stream is:

A. 2 kmph

B. 2.5 kmph

C. 3 kmph

D. 4 kmph

Solution:

Let the distance covered be x km and speed of stream = y kmph.
Speed downstream =

\frac{15}{2} + y

kmph
Speed upstream =

\frac{15}{2} - y

kmph

\begin{aligned} According to question, \\ \frac{2 x}{\frac{15}{2} + y} = \frac{x}{\frac{15}{2} - y} \\ o r, 15 - 2 y = \frac{15}{2} + y \\ o r, 3 y = 15 - \frac{15}{2} = \frac{15}{2} \\ o r, y = \frac{15}{6} = 2.5 kmph \end{aligned}

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