Question

speed of a boat in still water is 9km /hr . It goes 15 km
downstream and returns moving upstream in 3hrs 45 min.Find the speed of the stream

Answer 1

the speed of the stream will be 23 kms

Answer 2

Answer:

Speed of the stream is 3km/hr.

Step-by-step explanation:

Given : Speed of a boat in still water is 9km/hr . It goes 15 km downstream and returns moving upstream in 3hrs 45 min.

To find : The speed of the stream?

Solution :

T = time for downstream,

t = time for upstream travel.

T + t = 3 hrs 45 min = $\frac{15}{4}$ hrs.

For downstream,

$\frac{\text{Distance}}{\text{Speed}}=\text{Time}$

$\frac{15}{9+v}=T$....(1)

Similarly, For upstream,

$\frac{15}{9-v}=t$....(2)

Add (1) and (2)

$\frac{15}{9+v}+\frac{15}{9-v}=T+t$

$\frac{15\times 18}{81-v^2}=\frac{15}{4}$

$v^2=81-18\times4$

$v^2=9$

$v=3$

Therefore, Speed of the stream is 3km/hr.