9999/10000X7+1111/10000X27怎样使这个式子更简便?

9999/10000X7+1111/10000X27
=9999/10000X7+9999/10000X3
=9999/10000×10
=9999/10009999/10000×10这里为什么要*10？10怎么来的9999/10000X7+1111/10000X27=9999/10000X7+9999/10000X3=9999/10000×（7+3）=9999/10000×10=9999/10003捏?9999/10000X7+9999/10000X3=9999/10000×（7+3）乘法分配律啊哦。