The speed of a boat in still water is 8 km/hr. It covers a distance of 40 km upstream in 8 hours. What is the speed (in km/hr) of the stream?

Options

A. 2
B. 3
C. 4
D. `1.5`

Answer

To solve the problem, we need to find the speed of the stream given the speed of the boat in still water and the distance covered upstream.

### Step-by-step Solution:

1. **Identify the given values**:
- Speed of the boat in still water (B) = 8 km/hr
- Distance covered upstream (D) = 40 km
- Time taken to cover this distance (T) = 8 hours

2. **Calculate the effective speed of the boat upstream**:
The effective speed of the boat when going upstream can be calculated using the formula:
\[ \text{Effective Speed} = \frac{\text{Distance}}{\text{Time}} = \frac{40 \text{ km}}{8 \text{ hr}} = 5 \text{ km/hr} \]

3. **Set up the equation for upstream travel**:
When the boat is moving upstream, the effective speed is reduced by the speed of the stream (S). Therefore, we can express this as:
\[ \text{Effective Speed} = \text{Speed of Boat} - \text{Speed of Stream} \]
Substituting the known values:
\[ 5 = 8 - S \]

4. **Solve for the speed of the stream (S)**:
Rearranging the equation to find S:
\[ S = 8 - 5 = 3 \text{ km/hr} \]

5. **Conclusion**:
The speed of the stream is 3 km/hr.