Two donkeys are standing 400 metres apart. First donkey can run at a speed of 3m/sec and the second can run at 2m/sec. If two donkeys run towards each other after how much time (in seconds) will they bump into each other?

Options

A. 60
B. 80
C. 400
D. 40

Answer

To solve the problem of when the two donkeys will bump into each other, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Distance Between the Donkeys**:
The distance between the two donkeys is given as 400 meters.

2. **Determine the Speeds of the Donkeys**:
The speed of the first donkey is 3 meters per second (m/s), and the speed of the second donkey is 2 meters per second (m/s).

3. **Calculate the Relative Speed**:
Since the two donkeys are running towards each other, we can add their speeds to find the relative speed.
\[ \text{Relative Speed} = \text{Speed of Donkey 1} + \text{Speed of Donkey 2} = 3 \, \text{m/s} + 2 \, \text{m/s} = 5 \, \text{m/s} \]

4. **Use the Formula for Time**:
The time taken for the two donkeys to meet can be calculated using the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Relative Speed}} \]
Plugging in the values we have:
\[ \text{Time} = \frac{400 \, \text{meters}}{5 \, \text{m/s}} = 80 \, \text{seconds} \]

5. **Conclusion**:
Therefore, the two donkeys will bump into each other after 80 seconds.

### Final Answer:
The time after which the two donkeys will bump into each other is **80 seconds**.

---