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 ?

In an optical instrument, a convex lens of focal length 20 cm is used in combination with a concave lens of focal length 40 cm. What is the power of this combination?

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.

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is ..........

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:

What is the combined focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm ? What is the nature of the combined lens ?

A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 10 cm. What is the focal length and power of the combination ?