Help with optics problem involving diopters

[Altagyam]

Homework Statement

A nearsighted man uses his ideally prescribed contact lenses that have a refractive power of −3.60 diopters. He would like a prescription for eyeglasses. What is the correct eyeglasses prescription if he wears his eyeglasses a distance of 2.30 cm from his eyes?

Homework Equations

I used the mirror equation. 1/f = 1/d_o + 1/d_i

The Attempt at a Solution

I found a solution to be -3.32 and what I did was convert the refraction power to focus and then convert it to centimeters and added 2.3 and then did the inverse of that to obtain -3.32 and apparently that is wrong. I have used chegg and they show the same exact method I employed. I don't understand. Help!

 

[rude man]

If his contact lenses are "ideally prescribed" I take that to mean perfect vision at infinity. So does it matter what the refractive power of the contacts is?

 

[Altagyam]

If his contact lenses are "ideally prescribed" I take that to mean perfect vision at infinity. So does it matter what the refractive power of the contacts is?

I figured it out. I had to subtract 0.278 m - 0.023 m instead of adding. The correct answer was -3.92

 

[rude man]

I figured it out. I had to subtract 0.278 m - 0.023 m instead of adding. The correct answer was -3.92

OK, I misread the problem anyway ...