A thin lens has a focal length of `- 25 cm`. What is the power of the lens? It is convex or concave ?

A thin lens has focal length of, -25 cm. What is the power of the lens and what is its nature?

The focal length of a convex lens is 25 cm. What is its power?

A convex lens of focal length 25 cm is kept is contact with a concave lens of focal length 40 cm. What is the power of their combination ?

What is the power of a concave lens of focal length 25 cm ?