Question

A motor boat whose speed is 9 km/h in still water, goes 15 km down stream and comes back in a total time of 3 hours 45
minutes. Find the speed of the stream.

Answer 1

Step-by-step explanation:

T = time for downstream, t = time for upstream travel.

T + t = 3 hrs 45 min = 15/4 hrs.

For downstream, distance/velocity = time,

15/(V + v) = T

15/(9 + v) = T       ... (1)

Similarly,

15/(9 -  v) = t    ... (2)     ...where V - Speed of boat, v - speed of stream.

Add (1) and (2)

15/(9 + v) + 15/(9 -  v) = T + t

15(18)/(81 - v2)  = 15/4

v2 = 81 - (18x4) = 9

v = sped of stream is 3 km/hr.

HOPE THIS IS HELPFUL