The speed of a boat is 12 km/h in still water. It goes 18 km downstream and comes back in a total time of hours. Find the speed of the stream. (In km/h)
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 9.
Let the speed of the stream = x km/h
According to the given condition, we have:
18/(12 + x) + 18/(12 - x) = 48/7
Solving this by putting the options:
We can see it gets satisfied when we put x = 9:
⇒ 18/21 + 18/3 = 6/7 + 6 = 48/7
Hence,
Speed of stream = 9 km/h