To go a distance of 144 km upstream, a rower takes 12 hours while it takes her only 9 hours to row the same distance downstream. The speed of the stream is ______.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 2 km/h.
Let the speed of the boat in still water = b km/h
Speed of stream = s km/h
Upstream speed = b − s =144/12 = 12 km/h
Downstream speed = b + s = 144/9 = 16 km/h
b + s = 16
b − s = 12
Add the equations:
2 b = 28 ⇒ b = 14
Substitute into one equation:
14 + s = 16
⇒ s = 2
Speed of the stream = 2 kmph