A man swimming in a stream which flows 1 1/2 km / hr finds that in a given time he can swim twice as far with… · ABC26GN3812

Subject: General Aptitude · Chapter: Boats and Streams · Exam: M.A.T. 2008

A man swimming in a stream which flows $1 \frac{1}{2} \mathrm{km} / \mathrm{hr}$ finds that in a given time he can swim twice as far with the stream as he can against it. At what rate does he swim?

(a)$4 \frac{1}{2} \mathrm{km} / \mathrm{hr}$

(b)$5 \frac{1}{2} \mathrm{km} / \mathrm{hr}$

(c)$7 \frac{1}{2} \mathrm{km} / \mathrm{hr}$

(d)None of these

Answer

No answer key was printed for this question.

Explanation

Let speed upstream $=x \mathrm{km} / \mathrm{hr}$. Then, speed downstream $=2 x \mathrm{km} / \mathrm{hr}$. Speed of stream $=\frac{1}{2}(2 x-x) \mathrm{km} / \mathrm{hr}=\frac{x}{2} \mathrm{km} / \mathrm{hr}$. $$\therefore \quad \frac{x}{2}=1 \frac{1}{2} \Leftrightarrow \frac{x}{2}=\frac{3}{2} \Leftrightarrow x=3 .$$ So, speed upstream = 3 km/hr; Speed downstream $=6 \mathrm{km} / \mathrm{hr}$. Hence, rate of swimming $=\frac{1}{2}(3+6) \mathrm{km} / \mathrm{hr}=4 \frac{1}{2} \mathrm{km} / \mathrm{hr}$.

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