Question

A boat travels 24 km upstream in 6 hours and 30 km downstream in 5 hours. What is the speed of the boat in still water? 
 

• A. 6 km/h
• B. 5 km/h
• C. 7 km/h
• D. 8 km/h
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Hint:

In boat-stream problems, $b = \frac{\text{downstream speed} + \text{upstream speed}}{2}$.

Answer 1

The Correct Option is B

- Step 1: Find upstream speed - \[ \text{Upstream speed} = \frac{\text{Distance}}{\text{Time}} = \frac{24}{6} = 4 \ \text{km/h} \] 
- Step 2: Find downstream speed - \[ \text{Downstream speed} = \frac{30}{5} = 6 \ \text{km/h} \] 
- Step 3: Let boat speed in still water = $b$ and stream speed = $s$ - Then: \[ b - s = 4 \] \[ b + s = 6 \] 
- Step 4: Solve the system - Adding: $2b = 10 \implies b = 5$.