ABC26GN3810 · Boats and Streams

Subject: General Aptitude · Chapter: Boats and Streams · Exam: 2008 · Marks: · Difficulty:

A man can row $\frac{3}{4}$ of a km against the stream in $11 \frac{1}{4}$ minutes and returns in $7 \frac{1}{2}$ minutes. Find the speed of the man in still water.
(a)3 km/hr
(b)4 km/hr
(c)5 km/hr
(d)6 km/hr
Answer
Answer (as printed):
Explanation
Rate upstream $=\left(\frac{750}{675}\right) \mathrm{m} / \mathrm{sec}=\frac{10}{9} \mathrm{m} / \mathrm{sec}$; Rate downstream $=\left(\frac{750}{450}\right) \mathrm{m} / \mathrm{sec}=\frac{5}{3} \mathrm{m} / \mathrm{sec}$. $\therefore \quad$ Rate in still water $=\frac{1}{2}\left(\frac{10}{9}+\frac{5}{3}\right) \mathrm{m} / \mathrm{sec}=\frac{25}{18} \mathrm{m} / \mathrm{sec}=\left(\frac{25}{18} \times \frac{18}{5}\right) \mathrm{km} / \mathrm{hr}$ $=5 \mathrm{km} / \mathrm{hr}$.

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