初一计算题解法

（1+1/20+1/30）*（1/20+1/30+1/40）-（1+1/20+1/30+1/40）*（1/20+1/30）
=（1+1/20+1/30）*（1/20+1/30）+（1+1/20+1/30）*（1/40）-（1+1/20+1/30+1/40）*（1/20+1/30）
=（1+1/20+1/30-1-1/20-1/30-1/40）*（1/20+1/30）+（1+1/20+1/30）*（1/40）
=-1/40*（1/20+1/30）+（1+1/20+1/30）*（1/40）
=1/40*（1++1/20+1/30-1/20-1/30）
=1/40*1=1/40

分解开来啊
每个都相乘
1/20+1/30+1/40`````左边减右边``````1/20+1/30
+1/20^2```````````````````````````+1/20^2
+1/20*1/30`````````````````````````+1/20*1/30
+1/20*1/40````````````````````````+1/30*1/20
+1/30*1/20``````````````````````````+1/30^2
+1/30^2````````````````````````````+1/40*1/20
+1/30*1/40`````````````````````````1/40*1/30

可以发现很多可以消除``
只剩下1/40
答案就是这个``

1/20+1/30=1/12
1/20+1/30+1/40=13/120
原式=(1+1/12)13/120-(1+13/120)1/12=169/1440-133/1440=36/1440=1/40

1/40
用分配率很快的么……太懒了吧

1/40