dumb dumb

ok i don't beleive i'm asking but example: (-7)+(-18)= IT'S -25 RIGHT?

BUT WHEN YOU DO IT IN FRACTONS

LIKE: 5/12+(-1/4)

YOU FIND THE COMMON DENOMENATOR

WHICH IS 12 SO IT COMES OUT TO

5/12+ (-3/12)

AND YOU ANSWER IS POSITIVE 8/9

AND WHAT IF IT'S TWO NEGATIVES AND YOUR ADDING THEM DO YOU JUST ADD THEM? i'M SERIOUSLY CONFUSED AND DON'T KNOW WHY? gRR