Question

A transparent photographic slide is placed in front of a converging lens with a focal length of 2.41 cm. An image of the slide is formed 13.0 cm from the slide.
(a) How far is the lens from the slide if the image is real? (Enter your answers from smallest to largest starting with the first answer blank. Enter NONE in any remaining answer blanks.)(b) How far is the lens from the slide if the image is virtual? (Enter your answers from smallest to largest starting with the first answer blank. Enter NONE in any remaining answer blanks.)

Answer 1

1/q + 1/p = 1/f
q can be +13 or -13

Answer 2

I couldn't figure out a, but b is (1/2.41) - (1/-13) = 2.03 cm and the second blank is none.