题目内容

13、The average number of p，q，r is 4，and average number of p，q，r，x is 5，then x=
8
．
（英文词典：average number平均数）
分析：根据题意p，q，r的平均数是4，得出P+q+r=12，根据p，q，r，x的平均数是5，得出p+q+r+x=20，从而求出x的值．
解答：解：∵p，q，r的平均数是4，
∴P+q+r=4×3=12，
∵p，q，r，x的平均数是5，
∴p+q+r+x=5×4=20，
解得x=8．
故答案为：8．
点评：此题主要考查了平均数的求法，解决问题的关键是P+q+r=12，以及p，q，r，x的平均数是5，得出p+q+r+x=20，这种整体换元法在数学中经常用到．
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相关题目
Let a be the average of all odd prime numbers less than 50． The integer，most close to a is （　　）（英汉小字典：average平均值；odd prime numbers奇质数）
A、23B、24C、25D、26
阅读下面一则新闻，然后按要求写一篇１５０词左右的英语短文。
The headmaster of a middle school in southern England, David Hayes, has suspended（停课）students at his school 478 times over the past year—one in twenty of all the student suspensions in England.
Although some people believe that his actions go too far, he seems to be getting results. The number of students receiving “A” grades in the national senior school exam has increased from 48% in 2004 to 74% this year.
Mr Hayes says that many schools could achieves similar improvements if they improve their school students’ behavior. He also says the British government is wrong for pressuring schools not to suspend troublesome students and points out the harmful effects such students have on the quality of teaching and student learning. Suspensions often get many naughty students to improve their behavior, he says.
The school was below average in 2003. Mr Hayes joined the following year and now suspends two of the school’s 1880 students on average each school day. The total of 478 suspensions over the year means that almost one in four students have been punished this way. This year the school’s academic performance was judged as excellent.
【写作内容】
你在某英文报刊看到这则新闻后，准备就学生违纪的处理方式写一篇简评给该报编辑部，题目是“Should Schools Suspend Troublesome Students?”。内容要点包括：
1. 以约30词简要概括新闻内容：
2. 然后以约120词谈谈你的观点，内容包括：
（1）你是否支持该校长的做法，并陈述理由；
(2 ) 假设你是学校校长，谈谈你将如何处理违纪学生，并陈述理由。
【写作要求】
1. 可以使用实例或其他论述方法支持你的论点，也可参照阅读材料的内容，但不得直接引用原文的句子；
2. 作文中不能出现真实姓名和学校名称；
【评分标准】
概括准确，语言规范，内容合适，篇章连贯。
Let a be the average of all odd prime numbers less than 50． The integer，most close to a is （　　）（英汉小字典：average平均值；odd prime numbers奇质数）
A．23B．24C．25D．26
The average number of p，q，r is 4，and average number of p，q，r，x is 5，then x=______．
（英文词典：average number平均数）

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