2)(5/9-1/3)-1/6 4)(3/4-5/12)-1/5 6)(17/18-5/12)-2/9

2) (5/9-1/3)-1/6 = (10/18-6/18)-3/18 = 1/18
4) (3/4-5/12)-1/5 = (45/60-25/60)-12/60 = 8/60 = 2/15
6) (17/18-5/12)-2/9 = (34/36-15/36)-8/36 = 11/36

2)5/9-1/3=(5-3)/9 =2/9 ;  2/9-1/6=(4-3)/18= 1/18
4)3/4-5/12=(9-5)/12=4/12=1/3 ; 1/3-1/5=(5-3)/15=2/15   
6)17/18-5/12=(17-15)/36=2/36=-3/18=-1/6