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AS Level Question on Optics (Specifically Lenses)

"...A person wants to buy reading glasses so they can read a text clearly at a distance of 27.5cm from their eye. The min. focal length for this person's eye is 1.93cm and the distance from the centre of the lens to the retina is 2.0cm.

The available powers of lenses are +1.0D, +1.5D,+2.0D, +2.5D, +3.0D and +3.5D

show that the appropriate lens needed has a power of +2.0D. You may ignore the distance between then lens of the glasses and the eye."

anyone got any ideas on how to start/ approach this? cheers in advance, I can't seem to wrap my head around it