elef95
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A person cannot see objects that are located closer than 250 cm from his eyes. Calculate the type and the refractive power of the lenses that he must wear to correct for this condition. (The lenses will be mounted 2.0 cm in front of the person’s eyes.)

Can someone help me with this question please?
I know the person is hyperopic and a convex lens would be used to correct this condition.
I don't know how to get the focal length from the information given.
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elef95
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I have another question that I thought I was doing correctly. Can anyone explain this to me please?
In separate experiments, an object is placed 12.0 cm in front of two different mirrors: a flat mirror and a convex mirror. The image formed by the convex mirror is 4.0 cm closer to the mirror than the image formed by the plane mirror. Determine the focal length of the convex mirror.

The image distance of the flat mirror is 12cm. The image distance of the convex mirror is 8cm. Since the convex mirror forms virtual images this would be -8cm. Using the thin lens equation,
1/f = 1/do + 1/di. 1/12 - 1/8 = -0.0416
1/-0.0416 = -24cm = f

I have the answer for this question and it says that the image distance is -24cm and that the focal length is 4.8cm.
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elef95
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Anyone?
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