For example when you subtract 5 5/6 with 7 6/8 you have to check what does 6 and 8 have in common so 7 6/8 times 3/3 because that makes 24 and that is what 8 and 6 have in common so then you times 5 5/6 with 4/4 so you get 5 20/24 -7 18/24 but you have to regroup the 5 because the 7 is bigger so you cant subtract it so it turns into a 5 and
5 20/24 - 7 18/24
= (5 + 20/24) - (7 + 18/24)
= (5-7) + (20/24 - 18/24)
= -2 + 2/24
= -(2 - 2/24)
= -(1 24/24 - 2/24)
= -(1 22/24)
= -1 11/12
or, it might be easier to do the minus right at first, so
5 20/24 - 7 18/24
= -(7 18/24 - 5 20/24)
= -(6 42/24 - 5 20/24)
= -(1 22/24)
= -1 11/12