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?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 15.
Upstream speed = speed of boat - speed of stream
Downstream speed = Speed of boat + speed of stream
Speed of stream = 4.8 km/h
Upstream speed = Distance/Time
⇒ Speed of boat - 4.8 = 54/6
⇒ Speed of boat = 9 + 4.8 = 13.8 km/h
Downstream speed = Total distance/Time taken
⇒ 13.8 + 4.8 = 279/Time
Time = 279/18.6 = 15 hour