Eye lens focal length change to focus on object 1.69 m away

[haxxorboi]

Homework Statement

Suppose the lens in a human eye has far focal length equal to f0 = 40.1 mm, for distant objects to be in focus.
A. An object K is 1.69 m from the lens. How much should the focal length change to focus on the object K?

B.What is the magnification ( = image size divided by object size) for the object K?

Homework Equations

1/d_i+1/d_o=1/f

The Attempt at a Solution

A. 1/1690+1/x=1/40.1
x=41.0746 mm
Thus, delta f = .9746 mm but that's wrong for some reason... but it's been a long week...

B. -f₂/f₁=M

Can someone help me out here?

 

[tiny-tim]

1/1690+1/x=1/40.1
…
it's been a long week...

Hi haxxorboi!

Shouldn't the 1/x be on the other side?

 

[haxxorboi]

*sigh* Yep, that'd be the issue... need either more sleep or more caffeine I guess...

Problem solved.

Thank you very much... I'm going to go take a nap...