A lens forms real image of an object 20 cm away from lens. A second lens is kept in contact with this lens, then image shifts 10 cm towards the lens combination. Find the power of another lens.

Explanation

To solve the problem step by step, we can follow these steps:

### Step 1: Understand the Given Information
We have a lens (let's call it Lens 1) that forms a real image of an object placed 20 cm away from it. When a second lens (Lens 2) is placed in contact with Lens 1, the image shifts 10 cm towards the lens combination.

### Step 2: Define Variables
- Let the object distance for Lens 1 be \( u = -20 \) cm (the negative sign is used because the object is on the opposite side of the light direction).
- The initial image distance for Lens 1 is \( v_1 = 20 \) cm.
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