“盈亏”问题应用题，如按一般的思路分析，很难找到合适的解题方法。若根据题中的“相差”关系，往往可以发现这类题的解题规律。例１把铅笔分给若干个学生，若每人分３支则余７支；若每人分５支则少９支。问铅笔有多少支？学生有多少人？解：因为每个学生多给铅笔５－３＝２ “P & L” problem questions, such as the general idea of ​​the analysis, it is difficult to find a suitable solution to the problem. According to the title of the “difference”, you can often find the solution to these problems the law. Example 1 The pencil is divided into a number of students, if each divided into 3 and then more than 7; if each divided into 5 and then less 9. Ask pencil how many branches? How many students? Solution: Because each student to pencil 5-3 = 2