A person can row a distance of one km upstream in ten minutes and downstream in four minutes. What is the speed of the stream ?

Speed in still water = x km/h

Speed of current = y km/h

$herefore x+y=frac{1}{frac{4}{60}}=15$

$x-y=frac{1}{frac{10}{60}}=6$

$herefore$ Speed of current $=frac{1}{2}[(x+y)-(x-y)]$

$=frac{1}{2}(15-6)=frac{9}{2}=4.5 mathrm{~km} / mathrm{h}$