7/8 - 5/6 = 21/24 - 20/24 = 1/24

5 - 3 2/7 = 5 - 23/7 = 35/7 - 23/7 = 12/7

5/8 : 9/10 = 5/8 x 10/9 = 50/72 = 25/36

6 3/5 x 10 = 33/5 x 10 = 66