A boat covers a distance of 72 km downstream in 6 hours, while it takes 12 hours to cover the same distance upstream. What is the speed of the boat in still water?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 9 km/h.
Let the speed of a boat be x km/h and speed of the stream be y km/h.
Given that:
The boat covers the distance of 72 km downstream in 6 hours and it takes 12 hours to cover the same distance upstream.
According to the question
Downward speed = x + y = 72/6 = 12
⇒ x + y = 12 ....(1
Upstream speed = x - y = 72/12 = 6
⇒ x - y = 6 ...(2
Equation 1 + Equation 2:
⇒ 2x = 18
⇒ x = 9
Hence, the speed of the boat in still water is 9 km/h.