In one hour,a boat goes 11 km along the stream and 5 km against the stream. Then speed of the boat in still water (in km/hr) is :

Options

A. 3
B. 5
C. 8
D. 9

Answer

To find the speed of the boat in still water, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Information**:
- Distance traveled downstream (along the stream) = 11 km
- Distance traveled upstream (against the stream) = 5 km
- Time taken for both journeys = 1 hour

2. **Calculate the Speeds**:
- Speed downstream (D) = Distance downstream / Time = 11 km / 1 hr = 11 km/hr
- Speed upstream (U) = Distance upstream / Time = 5 km / 1 hr = 5 km/hr

3. **Use the Formula for Speed of the Boat in Still Water**:
- The formula to find the speed of the boat in still water (B) is:
\[ B = \frac{D + U}{2} \]
- Where D is the speed downstream and U is the speed upstream.

4. **Substitute the Values**:
- Substitute the values of D and U into the formula:
\[ B = \frac{11 + 5}{2} \]

5. **Calculate the Result**:
- Calculate the sum:
\[ B = \frac{16}{2} = 8 \text{ km/hr} \]

6. **Conclusion**:
- The speed of the boat in still water is 8 km/hr.

### Final Answer:
The speed of the boat in still water is **8 km/hr**.

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