4分之3/2分之1+5分之2
=3/4*2+2/5
=1.5+0.4
=1.9
1/3分之2+5分之3*3分之2
=1.5+0.5
=1.9
（7分之3++21分之11）*42
=3/7*42+11/21*42
=18+22
=40
2分之1/[(1-5分之2)/10分之1]
=0.5/[0.6/0.1]
=0.5/6
=1/12
(8分之7*12分之7+8分之7/5分之12)*3分之2
=7/8*(7/12+5/12)*2/3
=7/8*2/3
=7/12