0.28×8.6＋7.2×0.86
=0.28×8.6＋0.72×8.6
=(0.28＋0.72)×8.6
=1×8.6
=8.6
999×778＋333×666
=999×778＋999×222
=999×（778+222）
=999×1000
=999000