The speed of a boat in still water is 12 km/h. If the boat covers a distance of 38 km upstream in 4 hours, then the speed of the stream (in km/h) is:

Options

A. 6.5
B. 3.17
C. 2.5
D. 3

Answer

To solve the problem step by step, we will follow these calculations:

### Step 1: Understand the given information
- Speed of the boat in still water = 12 km/h
- Distance covered upstream = 38 km
- Time taken to cover this distance = 4 hours

### Step 2: Calculate the speed of the boat upstream
To find the speed of the boat while going upstream, we use the formula:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]

Substituting the values:
\[ \text{Speed upstream} = \frac{38 \text{ km}}{4 \text{ hours}} = 9.5 \text{ km/h} \]

### Step 3: Relate the speeds
The speed of the boat upstream can be expressed in terms of the speed of the boat in still water and the speed of the stream:
\[ \text{Speed upstream} = \text{Speed of boat in still water} - \text{Speed of stream} \]

Let the speed of the stream be \( x \) km/h. Therefore, we can write:
\[ 9.5 = 12 - x \]

### Step 4: Solve for the speed of the stream
Rearranging the equation to find \( x \):
\[ x = 12 - 9.5 \]
\[ x = 2.5 \text{ km/h} \]

### Conclusion
The speed of the stream is **2.5 km/h**.

---