简便计算6/7×5/9+4/9×6/7=6/7x(5/9+4/9)=6/7x1=6/7 0.8-（2/3+1/12）×8/9 =4/5-2/3x8/9-1/12x8/9=4/5-16/27-2/27=4/5-2/3=2/155/6÷（6-5/12-7/12)=5/6÷（6-1）=5/6÷5=1/6
