Answer with the Explanation:
ATQ, Distance in upstream =12km
Distance in downstream = 18 km
Let the speed in upstream = y km/hr
And the speed in downstream = x km/hr
Now, apply the formula.
Time = Distance/ speed
Or, (18/x) + (12/y) = 3………….. (i)
And (24/x) + (36/y) = 13/2……… (ii)
Now, multiply equation i by 3 to equate both equations.
(54/x) + (36/y) = 9………… (iii)
(24/x) + (36/y) = 13/2…….. (iv)
Now subtract equation iii by iv.
30/x = 9-13/2
Or, 30/x = 5/2
Or, 5x=60, i.e., x = 12
Now, put the value of x in equation i
(18/12) + (12/y) = 3
Or, 3/2 + 12/y = 3
Or, 12/y = 3-3/2
Or, 12/y = 3/2
Or, y = 8km/hr
Now, velocity of stream = (x-y)/ 2
= (12-8)/ 2 = 2km/hr.