Question

A boat covers a certain distance downstream in 3 hours and it covers the same distance upstream in 5 hours. What would be the speed of the stream if the speed of the boat in still water is 8 km/h?

• A. 3 km/h
• B. 2.5 km/h
• C. 2 km/h
• D. 1.5 km/h

Hint:

$S = B \times \frac{T_u - T_d}{T_u + T_d}$. Here: $8 \times \frac{5-3}{5+3} = 8 \times \frac{2}{8} = 2$.

Answer 1

The Correct Option is C

Step 1: Concept
Downstream speed = $B + S$; Upstream speed = $B - S$, where $B$ is boat speed and $S$ is stream speed.

Step 2: Analysis
Let stream speed be $s$. Distance $D$ is constant.
$D = (8+s) \times 3$ and $D = (8-s) \times 5$.

Step 3: Reasoning
$3(8+s) = 5(8-s)$
$24 + 3s = 40 - 5s$
$8s = 16 \Rightarrow s = 2$ km/h.

Step 4: Conclusion
The speed of the stream is 2 km/h. Final Answer: (C)