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## Homework Statement

It is desired to magnify reading material by a factor of 3.5× when a book is placed 9.5 cm behind a lens.

What is the power of the lens in diopters?

## Homework Equations

1/f = 1/di + 1/do

M = -di/do

P=1/f

## The Attempt at a Solution

I set equal the magnification to -di/do and solved for di

3.5=-di/9.5

di = -33.25 cm

Then I plugged into equation to find 1/f which = P

1/f = 1/di + 1/do

1/f = 1/-33.25 + 1/9.5

1/f = 0.075

I don't understand why this isn't right??