1) (1\12 + 1\6) : (3/8 - 1/4) =
(1/12+2/12):(6/16-4/16)=
1/4:1/8=1/4*8/1=2
2) (1 - 4\9) : (1\3 - 1\4)=
(9/9-4/9):(4/12-3/12)=
5/9:1/12=5/9*12/1=20/3=6 2/3
3) (1\3 - 5\16 ) : (1\6 - 1\8) =
(16/48-15/48):(4/24-3/24)=
1/48:1/24=1/48*24/1=1/2
4) ( 5\7 - 2\3) : (4\9 - 5\12)=
(15/21-14/21):(16/36-15/36)=
1/21:1/36=1/21*36/1=12/7=1 5/7