7.89*10.1
=7.89*（10+0.1）
=78.9+0.789
=79.689
(25+0.125)*0.8
=25*0.8+0.125*0.8
=20+0.1
=20.1
0.25*38.6*4
=（0.25*4）*38.6
=1*38.6
=38.6
3.2*10.2
=3.2×（10+0.2）
=32+0.64
=32.64