20-(1/2+1/3)/5/6*1.2=20-(5/6)/5/6*1.2=20-1.2=18.8
20-(1/2+1/3)/5/6×1.2= 20-(5/6)/5/6×1.2= 20-1/5/6= 20-1/30= 19 又 29/30
20-(1/2+1/3)/5/6*1.2=20-5/6×1.2/5/6=20-(5/6×6/5)/5/6=20-1/(5×6)=599/30
