Question

A man can row at $5$ km/hr in still water. If the river is running at $1$ km/hr it takes him $75$ minutes to row to a place and back. How far is the place ?

• A. $2.5$ km
• B. $3$ km
• C. $4$ km
• D. $5$ km

Answer 1

The correct option is B $3$ km

Let the distance to the place be $x$ km.
Speed downstream $=(5+1)$ km/hr $=6$ km/hr
Speed upstream $=(5-1)$ km/hr $=4$ km/hr
Given, $\frac{x}{6}+\frac{x}{4}=\frac{75}{60}$ hrs
$\Rightarrow \frac{2x+3x}{12}=\frac{5}{4}$
$\Rightarrow \frac{5x}{12}=\frac{5}{4}$

$\Rightarrow x=3$