Question Bank › General Aptitude › Boats and Streams › ABC26GN3812ABC26GN3812 · Boats and Streams Subject: General Aptitude · Chapter: Boats and Streams · Exam: 2008 · Marks: · Difficulty:
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 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 $=\frac{1}{2}(3+6) \mathrm{km} / \mathrm{hr}=4 \frac{1}{2} \mathrm{km} / \mathrm{hr}$.
← Previous in chapter · Chapter list · Next in chapter → Open in whiteboard · Browse this chapter in the app