Question

A man rows $\frac{3}{4}$ of a km against the stream in $11\frac{1}{4}$ minutes and returns in $7\frac{1}{2}$ min. Find the speed of the man in still water.

• A. $4$ km/hr
• B. $3$ km/hr
• C. $5$ km/hr
• D. $6$ km/hr

Answer 1

The correct option is C $5$ km/hr

Distance covered upstream in $\frac{45}{4}$ min $=\frac{3}{4}km$
$\therefore$ Speed of man upstream $=$ $(\frac{3}{4}\times \frac{4}{45}\times 60)$ km/hr $=4$ km/hr
Distance covered downstream in $\frac{15}{2}$ min $=\frac{3}{4}$ km
$\therefore$ Speed of man downstream $=$ $(\frac{3}{4}\times \frac{2}{15}\times 60)$ km/hr $=6$ km/hr
$\therefore$ Speed of man in still water $=$ $\frac{1}{2}(6+4)$ km/hr $=5$ km/hr