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
=2/15
5/6÷（6-5/12-7/12)
=5/6÷（6-1）
=5/6÷5
=1/6