An object is placed 30 cm away from a convex lens of focal length 10 cm and a sharp image is formed on a screen. Now, a concave lens is placed in contact with the convex lens. The screen now has to be moved by 45 cm to get a sharp image again. The magnitude of focal length of the concave lens is (in cm)

Options

(a) 72
(b) 60
(c) 36
(d) 20

Correct Answer:

20

Explanation:

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