20 men can do a work in 35 days. How many men are needed to complete the same work in 25 days.

Answer

To solve the problem, we can use the concept of work done, which is based on the formula:

\[ \text{Men} \times \text{Days} = \text{Work} \]

Given:
- 20 men can complete the work in 35 days.

We need to find out how many men (let's call this \( M_2 \)) are required to complete the same work in 25 days.

### Step-by-Step Solution:

1. **Calculate the total work done by the first group of men:**
\[ \text{Work} = \text{Men} \times \text{Days} = 20 \text{ men} \times 35 \text{ days} = 700 \text{ man-days} \]

2. **Set up the equation for the second scenario:**
We want to find \( M_2 \) such that:
\[ M_2 \times 25 \text{ days} = 700 \text{ man-days} \]

3. **Solve for \( M_2 \):**
\[ M_2 = \frac{700 \text{ man-days}}{25 \text{ days}} = 28 \text{ men} \]

4. **Conclusion:**
Therefore, 28 men are needed to complete the same work in 25 days.

### Summary of the Solution:
- **Total work**: 700 man-days
- **Men needed for 25 days**: 28 men