A person who can see things most clearly at a distance of `10 cm`. Requires spectacles to enable to him to see clearly things at a distance of `30 cm.` What should be the focal length of the spectacles ?

Explanation

To solve the problem, we need to determine the focal length of the spectacles required by a person who can see clearly at a distance of 10 cm but requires spectacles to see clearly at a distance of 30 cm. This condition indicates that the person is suffering from myopia (short-sightedness).

### Step-by-Step Solution:

1. **Identify the Given Information:**
- The nearest distance the person can see clearly (D) = 10 cm (this is the image distance, V).
- The distance at which the person wants to see clearly (U) = 30 cm (this is the object distance).

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