“神马都是浮云”同学问：(1/6+1/7+1/8)×(1/7+1/8+1/9)-(1/6+1/7+1/8+1/9)×(1/7+1/8)怎么计算？第二种问法，请问一下各位：（6分之1+7分之1+8分之1）*（7分之1+8分之1+9分之1）—（6分之1+7分之1+8分之1+9分之1)*（7分之1+8分之1）这道算式等于多少啊？应该有简便算法吧！有老师能告诉我方法吗？

数学题解答：此题算式较长，其中有些部分为几个分数相加，且多次出现，故可以用换元法来解决。设1/6+1/7+1/8＝a，则原式变成：

=（1/7+1/8+1/9）a-(a+1/9)×(1/7+1/8)

=(1/7+1/8+1/9)a-(1/7+1/8)a-(1/7+1/8)×1/9

=1/9a-(1/7+1/8)×1/9

此时再将a换回，变成1/6+1/7+1/8，这样算式又变成了：

=(1/6+1/7+1/8)×1/9-(1/7+1/8)×1/9

=1/6×1/9

=1/54

至此，已算出得数，主要用了换元法和乘法分配律解决了这个问题。

推荐阅读：
Important SEO Tips for E-commerce That You Cannot Disregard　 5 Effective Ways to Improve Blog Conversion Rate　 7 Reasons Blogging is Essential for Law Firms　 Should Your Blog Extend Into Multimedia Forms of Content?　 How Small Companies Can Use Big Data　 Hands Up and Step Slowly Away from the Keyboard: Why Good Execut　 How to Improve Bad Blog Posts　 5 Things That Bloggers Use in Their Craft　 How To Increase Your Ecommerce Sales Using Social Media　 Keyword Rank Tracking: What Newbie Bloggers Need to Know