Magnification of simple microscope is found to be 3 when image is formed at least distance for clear vision. What will be the magnification of simple microscope when final image is formed at infinity ?
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Explanation

To solve the problem, we need to understand the relationship between the magnification of a simple microscope and the position of the image formed.

### Step-by-Step Solution:

1. **Understanding Magnification**:
The magnification \( M \) of a simple microscope is given by the formula:
\[ M = 1 + \frac{d}{f} \]
where \( d \) is the least distance of distinct vision (approximately 25 cm) and \( f \) is the focal length of the microscope.

2. **Given Magnification**:
We are given that the magnification \( M \) is 3 when the image is formed at the least distance of distinct vision (25 cm):
\[ M = 3 \]
Substituting this into the magnification formula:
\[ 3 = 1 + \frac{d}{f} \]
Rearranging gives:
\[ \frac{d}{f} = 2 \]

3. **Finding Focal Length**:
Since \( d \) is 25 cm, we can find the focal length \( f \):
\[ \frac{25}{f} = 2 \implies f = \frac{25}{2} = 12.5 \text{ cm} \]

4. **Magnification at Infinity**:
When the final image is formed at infinity, the magnification \( M' \) is given by:
\[ M' = \frac{d}{f} \]
Substituting the value of \( f \):
\[ M' = \frac{25}{12.5} = 2 \]

5. **Conclusion**:
Therefore, the magnification of the simple microscope when the final image is formed at infinity is:
\[ M' = 2 \]

### Final Answer:
The magnification of the simple microscope when the final image is formed at infinity is **2**.

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