算一算
3/4+1/6=11/12 4/5-2/3=2/15 7/12+1/4= 5/6 1/2+3/8=7/8
1/2-3/8=1/ 8 5/6-3/10= 8/15 2/3-4/9=2/9 4/5-5/8=7/40