Question

My son is trying to figure out how to decompose 8/12 and what he has to work with is x/2 + x/2 =8/12

Answer 1

x/2 + x/2 = 2x / 2 or just x. So x = 8/12 which can be simplified by their greatest common factor of 4. Divide both top and bottom by 4. This gives you x = 2/3. 

Your answer for that equation is x = 2/3

Not sure what you mean by "decompose" though.