Question

a motorboat whose speed in still water is 9 km per hour goes 15 km downstream and come back to the same spot in a total time of 3 hour 45 minutes find the speed of the stream​

Answer 1

Answer:

3 km/hr

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 it was helpful