A man rows at the rate of 5 kmph in still water and his rate against the current is 3.5 kmph, then the man's rate along the current is:

Options

A. 4.25 kmph
B. 6 kmph
C. 6.5 kmph
D. 8.5 kmph

Answer

To solve the problem, we need to find the man's rate along the current (downstream speed) given his speed in still water and his speed against the current (upstream speed).

### Step-by-Step Solution:

1. **Identify Given Information:**
- Speed of the man in still water (B) = 5 km/h
- Speed against the current (upstream speed) = 3.5 km/h

2. **Understand the Relationship:**
- The speed against the current can be expressed as:
\[ \text{Upstream Speed} = \text{Speed in Still Water} - \text{Speed of the Current} \]
- This can be rearranged to find the speed of the current (S):
\[ S = B - \text{Upstream Speed} \]

3. **Calculate the Speed of the Current:**
- Substitute the known values into the equation:
\[ S = 5 \text{ km/h} - 3.5 \text{ km/h} = 1.5 \text{ km/h} \]

4. **Determine the Downstream Speed:**
- The downstream speed can be expressed as:
\[ \text{Downstream Speed} = \text{Speed in Still Water} + \text{Speed of the Current} \]
- Substitute the values:
\[ \text{Downstream Speed} = 5 \text{ km/h} + 1.5 \text{ km/h} = 6.5 \text{ km/h} \]

5. **Final Answer:**
- The man's rate along the current (downstream speed) is **6.5 km/h**.