4分之3减8分之3加2分之1 8分之3加9分之4减4分之1 4分之3加7分之5减8分之5

3/4-3/8+1/2=6/8-3/8+4/8=7/8
3/8+4/9-1/4=1/8+4/9=9/72+32/72=41/72
3/4+5/7-5/8=1/8+5/7=7/56+40/56=47/56
5/9-3/8+1/2=5/9+1/8=40/72+9/72=49/72