Without lenses, his near point is at 66.7 cm. In order to read a material at 50 cm, he needs a lens of 2.0D.
The near point is the closest distance of distinct vision. We can obtain the focal length from the power as in; f = 100/2.5 = 40cm
1/40 = -1/v + 1/25
1/v = 1/25 - 1/40
1/v = 0.04 - 0.025
v = 66.7 cm
Now if he wants to read at 50 cm
1/f = -1/50 + 1/25
1/f = 1/25 - 1/50
1/f = 0.04 - 0.02
f = 50cm
Power = 100/50 cm = 2 D
Learn more about power of a lens:https://brainly.com/question/1503351
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