A-man-can-row-a-boat-at-4-km-hr-in-still-water-He-row-the-boat-2km-upstream-and-2km-back-to-his-starting-place-in-2-hours-How-fast-is-the-stream-flowing-

Question Number 10069 by Tawakalitu ayo mi last updated on 23/Jan/17

A man can row a boat at 4 km / hr in still water .

He row the boat 2 km upstream and 2 km back

to his starting place in 2 hours . How fast is

the stream flowing .

Commented by ridwan balatif last updated on 23/Jan/17

Commented by Tawakalitu ayo mi last updated on 23/Jan/17

God bless you sir .

Answered by sandy_suhendra last updated on 23/Jan/17

let the velocity of the stream = x km / h

so the velocity upstream = (4 + x) km / h

the velocity when he rows back = (4 - x) km / h

the equation \Rightarrow \frac{2}{4 + x} + \frac{2}{4 - x} = 2

\frac{2 (4 - x) + 2 (4 + x)}{(4 + x) (4 - x)} = 2

\frac{8 - 2 x + 8 + 2 x}{16 - x^{2}} = 2

16 - x^{2} = 8

x^{2} = 8 \Rightarrow x = 2 \sqrt{2} km / h

Commented by Tawakalitu ayo mi last updated on 23/Jan/17

God bless you sir .