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 ?

Distance(D) is given as 1 km

Let the speed of boat and river be B km/hr and R km/hr

in case of upstream , the speed of boat = (B-R) km/hr

in case of downstream, the speed of boat = (B+R) km/hr

in upstream it takes 10 minutes to move 1 km and takes 4 minutes in downstream for the same distance

So , using distance = speed x time

$$\frac{1}{B-R}$$ = $$\frac{10}{60}$$

$$\frac{1}{B+R}$$ = $$\frac{4}{60}$$

B-R = 6 .....(1)

B+R = 15 .........(2)

Solving equations 1 and 2

B = 10.5 km/hr and R = 4.5 Km/hr