Speeds of a boat along the current and against the current are 14km/hr and 7km/hr respectively. What is the speed of boat (in km/hr) in still water?

Options

A. `3.5`
B. `7.5`
C. `10.5`
D. `9.5`

Answer

To find the speed of the boat in still water, we can use the information given about its speed along the current and against the current.

### Step-by-Step Solution:

1. **Define Variables**:
Let:
- \( x \) = speed of the boat in still water (in km/hr)
- \( y \) = speed of the current (in km/hr)

2. **Set Up Equations**:
From the problem, we know:
- Speed of the boat along the current: \( x + y = 14 \) km/hr
- Speed of the boat against the current: \( x - y = 7 \) km/hr

3. **Add the Two Equations**:
To eliminate \( y \), we can add the two equations:
\[ (x + y) + (x - y) = 14 + 7 \]
This simplifies to:
\[ 2x = 21 \]

4. **Solve for \( x \)**:
Divide both sides by 2:
\[ x = \frac{21}{2} = 10.5 \text{ km/hr} \]

5. **Conclusion**:
The speed of the boat in still water is \( 10.5 \) km/hr.