Two lenses of powers `-1.5 D` and `+2.75D` are kept in contact. Find the focal length of the combination.

Two lenses f powers-1.5 and +2.75 D are kept in contact.Find the focal length of the combination.

Two lenses of powers + 1.5 D and - 1 D are kept in contact. The focal length of the combination is

Two lenses of power 15.5 D and -5.5 D are placed in contact.What is teh focal length of the combbination?

Two lenses of local lengths 0.20m and 0.30m are kept in contact. Find the focal length of the combination. Calculate power of two and combination.

Two thin lenses of power +5 D and -2.5 D are in contact. What is the focal length of the combination ?

Two thin lenses of power +5 D and -2.5 D are in contact. What is the focal length of the combination ?

Two lenses of power - 15 D and + 5 D are in contact with each other. The focal length of the combination is

Two thin lenses of power 2D and -4D are kept in contact. What is the focal length of the combination in cm? (write the answer only)