Question

Total distance between A and B is d kms . If the distance travelled along the stream is three time of the total distance and the distance travelled against the stream is two times of the total distance . If the time taken to cover the distance along the stream is 10% less then the time taken to cover the distance against the stream .if a person cover a distance of 21 km in 1 hr 24 min along the stream , then find the rate of current ?
A. 2 km /hr
B. 3 km/hr
C. 1 km/hr
D. 4 km/hr

Answer 1

Correct Answer - B
Distance covered along the stream = 3d
Distance covered against the stream = 2d
Let speed of boat in still water = x km/hr
Let speed of current = y km/hr
`(21)/(x + y) = (7)/(5)`
`x +y = 15 " " … (i)`
And `(3d)/((x+y)) = (90)/(100) xx (2d)/(x - y)`
x - y = 9 `" " ... (ii)`
From (i) and (ii)
x = 12
y = 3
Rate of current = 3 km/hr