1) (1/12 + 1/6) : (3/8 - 1/4) = 1/4 : 1/8 = 2

2) ( 1 - 4/9) : (1/3 - 1/4) = 5/9 : 1/12 = 20/3

3) (1/3 - 5/16) : (1/6 - 1/8) = 1/43 : 1/24 = 24/43

4) ( 5/7 - 2/3) : (4/9 - 5/12) = 1/21 : 1/36 = 12/7