adding unlike denominators
5/6+2/5=
7/30
5/6-2/5=
7/30
4/7-5/6=
11/42
5/10+6/8=
10 /40
5/6-7/14=
10/42
5/7+5/9=
17/63
7/20-8/9=
97/180
7/8+4/9=
1 23/72
10/20+5/25=
70/100
10/12-5/10=
20/60
5/8+7/9=
67/72
5/7-7/10=
1/70
8/9-7/10=
17/90
10/15+15/20=
25/60
28/44-1/11=
48/88
7/9+3/4=
29/36
8/10-5/9=
22/90
8/10-7/9=
1 52/90
8/20+7/24=
60/100
1/2-3/8=
1/8
7/8+10/12=
17/24
10/15-8/20=
16/60
4/8-10/18=
4/72
7/20+8/24=
82/120
8/10-7/8=
3/40