Question

A man can row three-quarters of a kilometre against the stream in $11\frac{1}{4}$ minutes and can cover the same distance with the stream in $7\frac{1}{2}$ min. Find the speed (in km/hr) of the man in still water.

Answer 1

Rate upstream = $\left(\frac{750}{675}\right)$ m/sec = $\frac{10}{9}$ m/sec;
Rate downstream = $\left(\frac{750}{450}\right)$ m/sec = $\frac{5}{3}$ m/sec
$\therefore$ Rate in still water = $\frac{1}{2}(\frac{10}{9}+\frac{5}{3})$ m/sec
= $\frac{25}{18}$ m/sec = $(\frac{25}{18}\times \frac{18}{5})$ km/hr = 5 km/hr