Speed of man is 12 km/h in still water. If the rate of current is 4 km/h, then the effective speed of the man upstream is

Options

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

Answer

To solve the problem, we need to find the effective speed of a man swimming upstream when he has a certain speed in still water and there is a current flowing in the opposite direction.

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Speed of the man in still water (x) = 12 km/h
- Speed of the current (y) = 4 km/h

2. **Understand the Concept of Upstream Speed:**
- When a man swims upstream, he is moving against the current. Therefore, the effective speed of the man upstream is calculated by subtracting the speed of the current from the speed of the man in still water.

3. **Apply the Formula for Effective Speed Upstream:**
- Effective speed upstream = Speed of man in still water - Speed of current
- Mathematically, this can be represented as:
\[ \text{Effective Speed Upstream} = x - y \]

4. **Substitute the Values:**
- Substitute the values of x and y into the formula:
\[ \text{Effective Speed Upstream} = 12 \text{ km/h} - 4 \text{ km/h} \]

5. **Calculate the Effective Speed:**
- Perform the subtraction:
\[ \text{Effective Speed Upstream} = 12 - 4 = 8 \text{ km/h} \]

6. **Conclusion:**
- The effective speed of the man upstream is 8 km/h.

### Final Answer:
The effective speed of the man upstream is **8 km/h**.

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