in order to simplify this you need a common denominator. 15 works well for this. in order to keep the expression equivalent, we must multiply everything by the same thing, but we can format it in any way we like. we need to multiply everything by 1, but we can rewrite 1 by putting a number over itself, such as 5/5 and 3/3.
so we need to get both denominators to equal 15 but we can only multiply by 1. this means we need to multiply 4x/5 by 3/3 and 2x/3 by 5/5. when we do this we get 12x/15-10x/15
next, we simply combine like terms to get 2x/15 as our final answer
If she has 10/12 and uses 8/12 then you just subtract. Since the denominators are the same you just subtract 10-8 and get 2 the denominator is the same for your answers and so it is 2/12
