0.2[5/6除以（0.15+20/9）]
=0.2*[5/6÷427/180]
=1/5*5/6*180/427(约分)
=30/427
如果是0.15+9/20的话
0.2[5/6除以（0.15+9/20）]
=0.2*[5/6÷3/5]
=1/5*5/6*5/3(约分)
=5/18