Question

A man can row three-quarters of a kilometre against the stream in $11\frac{1}{4}$ minutes and covered 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 = $\frac{1}{2}(\frac{10}{9}+\frac{5}{3})m/sec$
$=\frac{25}{18}m/sec=(\frac{25}{18}\times \frac{18}{5})km/hr=5km/hr$