小学数学奥数基础教程三.docx

1、小学数学奥数基础教程三小学数学奥数基础教程(三年级)本教程共30讲第9讲 平均数把一个(总)数平均分成几个相等的数，相等的数的数值就叫做这个(总)数的平均数。例如，24平均分成四个数：6，6，6，6，数6就叫做24分成四份的平均数。又如，24平均分成六个数：4，4，4，4，4，4，数4就叫做24分成六份的平均数。由此可见，平均数是相对于“总数”和分成的“份数”而言的。知道了被均分的“总数”和均分的“份数”，就可以求出平均数：总数份数=平均数。“平均数”这个数学概念在我们的日常生活和工作中经常用到。例如，某次考试全班同学的“平均成绩”，几件货物的“平均重量”，某辆汽车行驶某段路程的“平均速度”等

2、等，都是我们经常碰到的求平均数的问题。根据求平均数的一般公式可以得到它们的计算方法：全班同学的总成绩全班同学人数=平均成绩，几件货物的总重量货物件数=平均重量，一辆汽车行驶的路程所用的时间=平均速度。我们在上一讲的例2中，已经接触到求平均数的应用题，下面再举一些例子来说明有关平均数应用问题的解法。例1一小组六个同学在某次数学考试中，分别为98分、87分、93分、86分、88分、94分。他们的平均成绩是多少？解：总成绩=988793868894546(分)。这个小组有6个同学，平均成绩是546691(分)。答：平均成绩是91分。例2把40千克苹果和80千克梨装在6个筐内(可以混装)，使每个筐装的

3、重量一样。每筐应装多少千克？解：苹果和梨的总重量为4080120(千克)。因要装成6筐，所以，每筐平均应装120620(千克)。答：每筐应装20千克。例3小明家先后买了两批小猪，养到今年10月。第一批的3头每头重66千克，第二批的5头每头重42千克。小明家养的猪平均多重？解：两批猪的总重量为663425408(千克)。两批猪的头数为358(头)，故平均每头猪重408851(千克)。答：平均每头猪重51千克。注意，在上例中不能这样来求每头猪的平均重量：(6642)254(千克)。上式求出的是两批猪的“平均重量的平均数”，而不是(35)8头猪的平均重量。这是刚接触平均数的同学最容易犯的错误！例4一

4、个学生为了培养自己的数学解题能力，除了认真读一些书外，还规定自己每周(一周为7天)平均每天做4道数学竞赛训练题。星期一至星期三每天做3道，星期四不做，星期五、六两天共做了13道。那么，星期日要做几道题才能达到自己规定的要求？分析：要先求出每周规定做的题目总数，然后求出星期一至星期六已做的题目数。两者相减就是星期日要完成的题目数。每周要完成的题目总数是47=28(道)。星期一至星期六已做题目331322(道)，所以，星期日要完成28-226(道)。解：47-(3313)6(道)。答：星期日要做6道题。例5三年级二班共有42名同学，全班平均身高为132厘米，其中女生有18人，平均身高为136厘米。

5、问：男生平均身高是多少？解：全班身高的总数为132425544(厘米)，女生身高总数为136182448(厘米)，男生有42-1824(人)，身高总数为5544-24483096(厘米)，男生平均身高为309624129(厘米)。综合列式：(13242-13618)(42-18)129(厘米)。答：男生平均身高为129厘米。例6小敏期末考试，数学92分，语文90分，英语成绩比这三门的平均成绩高4分。问：英语得了多少分？分析：英语比平均成绩高的这4分，是“补”给了数学和语文，所以三门功课的平均成绩为(92904)293(分)，由此可求出英语成绩。解：(92924)2497(分)。答：英语得了97

6、分。 练习91.一班有40个学生，二班有42个学生，三班有45个学生。开学后又转学来了11个学生。怎样分才能使每班学生人数相等？2.小岗计划4天做15道数学题，结果多做了9道。平均每天做了多少道？3.一小组同学体检量身高时发现其中2人的身高是123厘米，另外4人的身高均为132厘米。这个小组同学的平均身高是多少？4.小梅做跳绳练习，第一次跳了67下，第二次跳了76下。她要想三次平均成绩达到80下，第三次至少要跳多少下？5.一农机站有960千克的柴油。用了6天，还剩240千克。照此用法，剩下的柴油还可用几天？6.小浩为培养自己的阅读能力，自己规定这一个月(30天)要读完共288页的彩图世界童话名

7、著伊索寓言。头9天平均每天读了8页，第二个9天平均每天读了10页，第三个9天平均每天读了11页。最后三天平均每天需要读几页才能达到自己规定的要求？7.五个同学期末考试的数学成绩平均94分，而其中有三个同学的平均成绩为92分，另两个同学的平均成绩是多少？8.小亮学游泳，第一次游了25米，第二次游的距离比两次游的平均距离多8米。小亮第二次游了多少米？9.篮球队中四名队员的平均身高是182厘米，另一名队员的身高比这五队员的平均身高矮8厘米，这名队员的身高是多少？答案与提示练习91.一、二、三班分别转入6，4，1人。提示：每班应有(40424511)346(人)。2.6道。解：(159)4=6(道)。

8、3.129厘米。解：(12321324)6=129(厘米)。4.97下。解：803(6776)97(下)。5.2天。解：240(960240)62(天)。6.9页。解：288(81011)939(页)。7.97分。解：(945923)297(分)。8.41米。解：258241(米)。9.172厘米。解：这名队员比平均身高矮的这8厘米，是由另四名队员给“补上”的，所以平均身高为18284180(厘米)，这名队员身高1808172(厘米)。Class: Name: ( )1. Good morning! !A.Morning ! B.Hello ! C.Hi !( )2. Nice to see

9、you again ! .A.How are you ? B.Nice to see you , too . C.How do you do ?( )3.Good night,mom ! A.Night ! B.Good night ! C.Good evening .( )4.How do you do ? A.How are you ? B.Fine,thanks . C.How do you do ?( )5.How many story books do you have ? A.I have 10. B.I can see 10. C.Thirty yuan.( )6.Do you

10、have new teachers? A.Yes,we do . B.Yes,we dont. C.Yes,we have .( )7.Whos your art teacher ? A.Mr Zhu. B.Miss Zhu. C.Hes tall.( )8.Whats he like? A.Hes tall and strong . B.Yes,he is. C.Mr Zhu.( )9.Is your English teacher young? A.No,she isnt. B.Yes,she is . C.No,she is.( )10. ? Her name is Chen Jie.A

11、.Whats your name ? B.Whats she name ? C.Whats her name ?( )11. ? I like Chinese,math and English.A.What classes do you like? B.What do you like? C.What are you like ?( )12. ? We have English and P.E.A.What do you have on Mondays ? B.What do you have ?C.What do you have on Monday?( )13. ? Its Monday.

12、A.What is it today ? B.What day is it today ? C.What day is today ?( )14. ? I watch TV and do my homework.A.What do you do ? B.What do you do in Mondays? C.What do you do on Sundays ?( )15.May I have a look ? A.Sure.Here you are . B.Look ! C.Here you are .( )16.Our math teacher is Canada.A.from B.in

13、 C.at ( )17.I three new teachers.A.has B.am C.have( )18.Whats Chinese teacher like ?A.you B.your C.youre( )19.My P.E.teacher is thin.A.too B.so C.very ( )20.There are days in a week.A.six B.seven C.eight ( )21.There are month(月)in a year(年).A.ten B.eleven C.twelve( )22.I often watch TV Saturday .A.o

14、n B.in C.at ( )23.I like P.E. I dont lime music.A.but B.and C.so( )24.This is apple. It is red apple.A.a , a B.an,an C.an, a( )25.What do you like ?A.classes B.class C.classs六年级英语测试题Class: Name: ( )1. How are you ? A.Fine,thanks. B.Yes,it is. C.How are you ?( )2. Nice to meet you ! A.Fine,thank you.

15、 B.OK. C.Nice to meet you ,too !( )3. How do you go to school ? A.I go to Canada by plane. B.I go to school by bike. C.What about you ?( )4. How do you go to the USA ? A.I usually go to school by bus. B.I go to England by ship. C.I go by plane.( )5. ? My home is near the post office.A. Where is your

16、 home ? B.OK. C.See you then!( )6. See you at 2 oclock. A.See you then ! B.The fifth floor. C.Its easy.( )7. ? You can go by the No.15 bus.A.Its not far. B. How can I get to Zhongshan Park ? C.Sure.( )8. Where is the hospital? A.Next to the cinema. B.Thank you . C.Youre welcome.( )9. Excuse me ,is t

17、here a cinema near here ? A.Yes,there is . B.No,its not far. C.Its near the post office.( )10.? ? Its near the post office.A.Yes,there is . B.No,its not far. C. Where is the library? ( )11. ? Its next to the hospital. A. Where is the cinema ,please ? B.Is it far ? C.Go straight.( )12. How can I get

18、to the hospital ? A.Its next to the hospital. B.You can go by the No.201 bus. C.Thank you.( )13.Thank you . A.Thank you . B.OK. C.Youre welcome.( )14. How can I get to the museum? A.Go straight.Then turn left. B.Thank you . C.Its east of the cinema .( )15. Where is the post office ? A.Go straight.Th

19、en turn left. B.Thank you . C.Its east of the cinema .( )16. What are you going to do this evening ? A.Im going to the cinema . B.I go to school on foot. C.Yes,it is.( )17. Is it far ? A.No,it is . B.Yes , it is . C.Yes,it isnt.( )18. do you go to school ?A.What B.Where C.How( )19. I go to school bi

20、ke.A.on B. by C.get( )20. Can I go foot ?A.by B.at C.on( )21.How can I to the post office ?A.near B. get C.for( )22. me.A. Excuse B. How C.next ( )23. birthday to you !A. After B.Happy C.First( )24. The hospital is the left.A. at B.in C.on ( )25. is the bookstore ?A.Where B.How C.When 四年级英语测试题Class:

21、 Name: ( )1.Good afternoon ! A.Hello! B.Hi ! C.Afternoon !( )2.Nice to see you again ! A.How are you ? B.Hello ! C.Nice to see you , too.( )3.Good night,moom ! A.Good evening ! B.Good night ! C.Night !( )4.How are you ? A.Fine,thank you . B.I am 10. C.Nine .( )5.How do you do ? A.Fine ,Thank you . B

22、.How are you ? C.How do you do ?( )6.How old are you ? A.How are you ? B.I am 11. C.I have 11.( )7. ? I have 23.A.How many books do you have ? B.How many books can you see?C.How many book do you have ?( )8. ? I can see 6.A.How many lights do you have ? B.How many lights can you see ?C.How many light

23、 can you see ?( )9.May I have a look ? A.Sure.Here you are . B.Look! C.Sure.Here are you .( )10. ? 50 yuan. A.How much is this schoolbag ? B.How many is this schoolbag ?C.How much are this schoolbag ?( )11.Wheres my seat ? A.Its near the door. B.Its on the door. C.Its under the door.( )12.Lets clean

24、 the desks and chairs. A.All right ! B.Hello ! C.Its nice .( )13.Whats this ? A.There is a board . B.Its a bee. C.Its bee.( )14. ? My name is Mike.A.Here are you ? B.Whats your name ? C.How do you do ?( )15.Whos the inventor of paper ? A.Chinese people. B.Oh! Great ! C.Hello!( )16.I a student. You a teacher.A.am ,am B.are, are C.am, are ( )17.This a boy.His name Zhang Peng.A.is, is