Physics Lens Problem: Find Object Distance

[meermeeronthewall]

Homework Statement

An object and its lens-produced real image are 2.4 m apart.

Part A
If the lens has 55-cm focal length, what are the possible values for the object distance?
Express your answer using two significant figures.

Homework Equations

1/s+1/s'=1/f
s-s'=2.4m

The Attempt at a Solution

1/s+1/(s-2.4)=1/.55
2s-2.4/s^2-2.4s=1/.55
s^2-3.5s+1.32=0
I then used the quadratic formula and found:
s=3.07 and s=.4299

I tried this answer, but it is wrong. I also tried substituting s'=2.4+s. But the answers I got for that were wrong as well.

Nevermind, I solved it. I had to use s-(-s')=2.4.

 

[BvU]

Hello m², nevertheless.

Maybe it helped that you had to order your thoughts to come up with a good first post in PF