The difference between downstream speed and upstream speed of boat is 8 km/hr and boat travels 90 km from A to B (downstream) in 6 hours . Then find the speed of boat in still water ?

Options

A. 11 km/hr
B. 18 km/hr
C. 20 km/hr
D. 16 km/hr

Answer

A

Explanation

Let the speed of boat in still water be x km/hr and that of stream be y km/hr
ATQ , `(x + y) - (x - y) = 8`
`implies 2y = 8 implies y = 4` km/hr
Downstream speed = `(x + y) = (90)/(6) = 15` km/hr
`implies x = 11` km/hr