Question

a motor boat whose speed is 15kmph in still water goes 30km downstream and comes back in a total of 4 hours 30 minutes. find the speed of the stream.

Answer 1

Let the speed be x km/hr.

Then the downstream speed will be 15+x and upstream speed will be 15-x.

Given, 30/15+x - 30/15-x = 4 1/2

            900/225-x^2 = 9/2

           9x^2 = 225

             x^2 = 25

              x = 5km/hr.


Hope this helps!

Answer 2

speed of boat = 15km/hr
speed of stream = x
downstream= boat's speed + stream's speed
upstream= boat's speed - stream's speed
30×2/9 = 15 -x
x=15-20/3
x=25/3 is speed of stream