If the speed of a boat in still water is 20 km/hr and the spedd of the current is 5 km /hr , then the time taken by the boat to travel 100 km with the current is :

Options

A. 2 hours
B. 3 hours
C. 4 hours
D. 7 hours

Answer

To solve the problem step by step, we need to determine the time taken by the boat to travel 100 km with the current. Here’s how we can do it:

### Step 1: Identify the speeds
- Speed of the boat in still water = 20 km/hr
- Speed of the current = 5 km/hr

### Step 2: Calculate the downstream speed
When the boat is moving downstream (with the current), the effective speed of the boat is the sum of the speed of the boat in still water and the speed of the current.
- Downstream speed = Speed of the boat + Speed of the current
- Downstream speed = 20 km/hr + 5 km/hr = 25 km/hr

### Step 3: Use the formula for time
The formula to calculate time is:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} \]

### Step 4: Substitute the values into the formula
- Distance = 100 km
- Speed (downstream) = 25 km/hr

Now, substituting these values into the formula:
\[ \text{Time} = \frac{100 \text{ km}}{25 \text{ km/hr}} \]

### Step 5: Calculate the time
\[ \text{Time} = 4 \text{ hours} \]

### Final Answer
The time taken by the boat to travel 100 km with the current is **4 hours**.

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