Subject: General Aptitude · Chapter: Boats and Streams · Exam: 2009 · Marks: · Difficulty:
A man can row $7 \frac{1}{2} \mathrm{kmph}$ in still water. If in a river running at 1.5 km an hour, it takes him 50 minutes to row to a place and back, how far off is the place?
Answer
Answer (as printed):
Explanation
Speed downstream $=(7.5+1.5) \mathrm{kmph}=9 \mathrm{kmph}$; Speed upstream $=(7.5-1.5) \mathrm{kmph}=6 \mathrm{kmph}$. Let the required distance be $x \mathrm{km}$. Then, $$\frac{x}{9}+\frac{x}{6}=\frac{50}{60} \Leftrightarrow 2 x+3 x=\left(\frac{5}{6} \times 18\right) \Leftrightarrow 5 x=15 \Leftrightarrow x=3 .$$ Hence, the required distance is 3 km .