8.9*9.9
=8.9*(10-0.1)
=89-0.89
=88.11
0.02*38.7 *50
=38.7*0.02*50
=38.7*1
=38.7
1.25*（8+0.8）
=1.25*8+1.25*0.8
=10+1
=11