Question

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

Answer 1

Answer:

2.83km/hr

Explanation:

Let stream flowing at the rat x km/hr

In still water

Speed of boat=4km/hr

Upstream speed=4-x

Downstream speed=4+x

Total time=2 hr

Time=Distance/speed

According to question

$\frac{2}{4+x}+\frac{2}{4-x}=2$

$\frac{8-2x+8+2x}{(4+x)(4-x)}=2$

$\frac{16}{4^2-x^2}=2$

Using the formula

$(a+b)(a-b)=a^2-b^2$

$4^2-x^2=\frac{16}{2}$

$16-x^2=8$

$16-8=x^2$

$8=x^2$

$x=\sqrt{8}=2.83km/hr$

Hence, the stream  is flowing at 2.83km/hr