A man rows 15 km downstream in 1 hour 15 minutes and rows back the same 15 km upstream in 2 hours 30 minutes. What is his rowing speed in still water?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 9 km/hr
The speed in still water is half the sum of the downstream and upstream speeds, because the stream is added on one leg and taken away on the other.
Downstream speed \(\displaystyle =\frac{15}{1.25}=12\) km/hr
Upstream speed \(\displaystyle =\frac{15}{2.5}=6\) km/hr
Speed in still water \(\displaystyle =\frac{12+6}{2}=9\) km/hr