5/12-7/18=15/36-14/36=1/36
17/21+3/4-1/2+4/21=17/21+4/21+3/4-1/2=1+1/4=5/4
16/31+6/31+15/31=16/31+15/31+6/31=1+6/31=37/31
4/7+17/24-4/7=17/24
5/12-7/18=15/36-14/36=1/36
17/21+3/4-1/2+4/21=17/21+4/21+3/4-1/2=1+1/4=5/4
16/31+6/31+15/31=16/31+15/31+6/31=1+6/31=37/31
4/7+17/24-4/7=17/24