A convex lens has 9 cm focal length and a concave lens has – 18 cm focal length. The focal length of the combination in contact will be

A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is

A convex lens of focal length x and a concave lens of focal length y are placed in contact. The focal length of the combination is

A convex lens of focal length A and a concave lens of focal length B are placed in contact. The focal length of the combination is

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

A convex lens of focal length f_1 and a concave lens of focal length f_2 are placed in contact. The focal length of the combination is f. Then

A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm. 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:

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are joined together. The power of the combination will be