15/31 = 1 - 16/31
83/99 = 1 - 16/99
Do 16/31 > 16/98 nên 1 - 16/31 < 1 - 16/99
Vậy 15/31 < 83/99
----------------------------
19/60 = 95/300
27/100 = 81/300
Do 95 > 81 nên 95/300 > 81/300
Vậy 19/60 > 27/100
---------------------------
3/8 = 21/56
4/7 = 32/56
Do 21 < 32 nê 21/56 < 32/56
Vậy 3/8 < 4/7