Contact lenses, focal length and uncorrected far point distance

[danok]

1. A nearsighted person wears contacts with a focal length of -7.6cm. If this person's far point distance with her glasses is 8.7m, what is her uncorrected far point distance?



2. 1/F=1/d_o+1/d_i



3. 1/-7.6=1/d_o+1/870
=-7.534

I am completely lost here...please help. Thanks!

 

[danok]

So it's not just me then...

 

[mgb_phys]

The image distance is constant in both cases (the length of the eyeball)
You have an unknown focal length lens (the eye) and a combintion of the same unknown lens and a known lens with a known object distance.

So write the equations for object, image distance and focal length for both cases.