4分之3*9分之8+3分之1
=3分之2＋3分之1
=1
2/9*10-2/9
=9分之2×9
=2
（3/5+9/10）*5/6
=3/2×5/6
=5/4
7/8*4/15*8
=28/15
（3/4*8/9）*16
=2/3×16
=32/3
8/9*8+8/9
=8/9×9
=8
120*（1/2+1/3+1/4）
=120×2分之1＋120×3分之1＋120×4分之1
=60＋40＋30
=130
1/5*7/12+1/5*5/12
=1/5×【7/12＋5/12】
=1/5×1
=1/5