Solving a convex mirror problem

[Jack.P]

Homework Statement

Given the following information: convex mirror, focal length (f) = 12.5 metres, height object (h_o) = 5 metres, height image (h_i) = 1 metre. Find distance object (d_o) and distance image (d_i).

Homework Equations

1/f = 1/d_o + 1/d_i

Magnification= -h_i/h_o = d_i/d_o

The Attempt at a Solution

I found that the magnification is -0.2.

Rearranging the magnification equation I found that d_i=-0.2do
and that
do=-5d_i

My intention was to substitute one of the two into 1/f = 1/d_o + 1/d_i

I tried to make the denominators equal after substituting in d_i=-0.2do however my answer was incorrect.

Correct answers are d_o = 50 metres, d_i = -10 metres

I don't understand how to mathematically solve this problem. Any help would be greatfully appreciated.

 

[paisiello2]

What was your answer?

I think your approach was right so maybe you just made an arithmetic mistake.