3.82*9.9+0.382=37.818+0.382=38.2。
0.27乘九点九加零点0.027
=0.027*99+0.027
=0.027*(99+1)
=0.027*100
=2.7
1.87×9.9+0.187
=0.187×99+0.187
=0.187×(99+1)
=0.187×100
=18.7
0.9+9.9+99.9+999.9+0.4
=1-0.1+ 10 - 0.1 + 100-0.1 + 1000-0.1 +0.4
=1111
7.74×(10-0.1)+0.774
=7.74×10-7.74×0.1+0.774
=77.4-0.774+0.774
=77.4
19.4×0.9+0.1×16.4
=(3+16.4)×0.9+0.1×16.4
=3×0.9+16.4×0.9+0.1×16.4
=2.7+16.4×(0.9+0.1)
=2.7+16.4
=19.1
101×9.9+101×0.1
=101×(9.9+0.1)
=101×10
=1010
=5.7*9.9+0.57
=5.7*9.9+5.7*0.1
=5.7*(9.9+0.1)
=5.7*10
=57
0.5x9.8x2=0.5x2x9.8
用了乘法交换律
乘法交换律用字母表示:a b=b a
这里9.8x2变成了2x9.8
0.5x2比较简便
所以运用了乘法交换律
3.84×9.6+0.96×61.6
=3.84×9.6+9.6×6.16
=(3.84+6.16)×9.6
=10×9.6
=96