A boat can go 54 km upstream in 6 hours. If the speed of the stream is 4.8 km/h, then how much time (in hours) will the boat take to cover a distance of 279 km downstream?

Options
a) 18
b) 15
c) 16
d) 20

Solution

As per question
Boat can go 54 km upstream in 6 hours
Speed of the upstream = $ \frac{\text{54 km}}{\text{6 hour}}$ = 9 km/h
Speed of the stream is 4.8 km/h
Speed of the boat = 4.8 km/h + 9 km/h = 13.8 km/h
Speed of the downstream = 13.8 km/h + 4.8 km/h = 18.6 km/h
Time will the boat take to cover a distance of 279 km downstream?
Time = $ \frac{\text{Distance}}{\text{Speed}}$
Time = $ \frac{279}{18.6}$
Time = 15

Ans: 15