Question

A man can row 4.5 km/hr in still water and he finds that it takes him twice as long to row up as to row down the river. Find the rate of the stream.

Answer 1

let rate of the stream =x km /h
upstream speed of boat=(4.5-×) km/hr
downstream speed of boat=(4.5+×) km/hr
let distance =D km
Time taken upstream =D/(4.5-×)
Time taken downstream =D/(4.5+×)
D/(4.5-×)=2D/(4.5+×)
(4.5+×)=2(4.5-×)
(4.5+×)=9-2x
3x=4.5
x=1.5km/hr

Answer 2

Answer:

Rate of stream=1.5km/hr

Step-by-step explanation:

Let the speed of the water=x$\frac{km}{hr}$,

The upward speed of the water=$(4.5-x)\frac{km}{hr}$,

The downward speed of the water=$(4.5+x)\frac{km}{hr}$

Let the distance be =y, then

Time rowing toward up=2× time rowing towards down

$\frac{y}{(4.5-x)}=2{\times}\frac{y}{(4.5+x)}$

$4.5y+xy=9.0y-2xy$

$3x=4.5$

$x=1.5\frac{km}{hr}$