If a person can sees clearly at a distance of 100 cm, then find the power of leris used to see object at 40 cm.

Explanation

To solve the problem step by step, we will use the lens formula and the concept of power of a lens.

### Step 1: Understand the given data
- The person can see clearly at a distance of 100 cm. This means that the farthest point they can see clearly (the far point) is at 100 cm, which we can denote as the image distance (V = -100 cm, negative because it is a virtual image).
- The object distance (U) for which we want to find the power of the lens is at 40 cm (U = -40 cm, also negative for the same reason).

### Step 2: Use the lens formula
The lens formula is given by:
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