A converging lens of focal length 40 cm is kept in contact with a diverging lens of focal length 30 cm. Find the focal length of the combination.

Explanation

To find the focal length of the combination of a converging lens and a diverging lens placed in contact, we can use the formula for the focal length of two lenses in contact:

\[ \frac{1}{f} = \frac{1}{f_1} + \frac{1}{f_2} \]

Where:
- \( f \) is the focal length of the combination,
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