How to achieve a desired result by reducing numerator and denominator simultaneously

Hi, hopefully someone can help, am not all that mathematically minded!!

If I have the following

Numerator 300

Denominator 250

Divide them I get

1.2

I need to attain a result of 1.25. How can I calculate the minimum amount to subtract off both to attain this result. If I take 1 off the numerator I must take 1 off the denominator, if 2 off the numerator then 2 off the denominator and so on.

Any help greatly appreciated, are there excel functions to these effect? add ins?