A person having a myopic eye uses a concave lens of focal length 20 cm. What is the power of the lens?

A man used a concave lens of focal length 20cm.Find the power of the lens.

Find the power of a concave lens of focal length 2 m ?

Find the power of a convex lens of focal length 25 cm.

What is concave lens ?

a concave lens of focal length 20cm is placed in contact with a convex lens of focal length 40cm. Find the power of the combination.