有红黄两种颜色的小球共140个，拿出红球的1/4，再拿出7个黄球，剩下的红球和黄球正好－样多。原来红球和黄球各有多少个？

数学题解答：题中有红黄两种小球，且告诉了它们的总数，要求两种小球各有多少个。另外，题中还有“剩下的红球与黄球一样多”的等量关系，所以用方程解答比较容易。

解：设黄球有x个，则红球有（140-x）个。

红球拿起了1/4，还剩下3/4，所以剩下的红球可表示为：(140-x)×（1-1/4），剩下的黄球可表示为x-7，它们是相等的关系。列方程为：

(140-x)×（1-1/4）＝x-7

（140-x）×3/4        =x-7

                140×3/4  -3/4x=x-7

                                 7/4 x-7=105

                                       7/4x=105+7

                                      7/4x=112

                                               x=64

黄球有64个，红球有：140-64＝76（个）。

推荐阅读：
Facebook’s “Dislike” Button Isn’t a Dislike Button At All　 Making Money at Home: Blogging vs. Content Writing　 Back to the Basics: How to Get More Twitter Followers　 Trump Steals Spotlight During Democratic Debate　 Dorsey’s 8% Twitter Layoff　 Finding Out Which Content Is Unacceptable For Your Website　 The Custom Sort String Algorithm with Count and Write　 Algorithms to Count the Number of Palindromic Substrings　 Depth First Search Algorithm to Find Leaves of a Binary Tree　 Understanding The Math Before Investing In Stocks