Fractions with negative denomanators and fractions with negative symbol beside it...

First: I needa know what i do if i have a common denomaintor of Eg. 2/4+ 2/-4 What do i do?.. do i replace the negative and put it on the numerator ????

Second: When i have fractions like .... - 2/3+ 3/5 do i put it automatically on the numerator or do i find the answer first and then put it on the numertor?.... PLease help :) Math quiz tomorrow

2/- 4 = - 2/4 = - 1/2

now

2/4 + 2/ - 4 =

2/4 - 2/4 = 0/4 =0 since the fractions have the same denominator we simply subtract

- 2/3 + 3/5 =

the common denominator is 3 x 5 = 15 the negative goes with the whole fraction not just the numerator or the denominator.

so we get

- 10/15 + 9/15 = - 1/15