A man rows 15 km upstream in 5 hours and 25 km downstream in 5 hours each time, then the speed of the stream is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 1 km / hour **
Upstream speed = $\frac{15}{5} = 3$ km/hr
Downstream speed = $\frac{25}{5} = 5$ km/hr
Let boat speed in still water = $b$, stream speed = $s$.
Upstream: $b - s = 3$
Downstream: $b + s = 5$
Add both:
$2b = 8 \Rightarrow b = 4$
Substitute:
$4 - s = 3 \Rightarrow s = 1$
Speed of stream = 1 km/hr