Question

A boat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is ___ km/hr. Type your answer below!

Answer 1

Answer:

Ans is 5 km

Step-by-step explanation:

Let speed of stream is x km/hr

the total distance is 30 kms.

Speed of boat in still water is 15 km/hr.

So in downstream

speed of boat (15+x)

time taken

to travel 30 kms is 30/(15+x)hrs.

In upstream speed is (15-x)

so time taken

to travel 30 kms is 30/(15-x)

total time taken by boat

30/(15+x)+30/(15-x)=4+1/2

30(15-x)+30(15+x)=9(225-x^2) /2

450+450=(2025–9x^2)/2

1800=2025–9x^2

9x^2 =225

3x=15

x=5 km/hr