12月27日数学机井总结

lisaislisa

well done! [em2]
margland , I should learn from you to update JJ day by day as long as I am on duty again...

In addition here is another JJ I met
两组统计数字：
Total number         Mean        Median
I             82            85   
II            79            78
Question: the mean of both II and I is larger than the median of both II and I?
A:    I+II=89
B:    I=42, II=37

my answer is B
is that so ?

^^

robert

45。DS: two classes, A and B，下面是一张有关考试成绩的表格
mean medium
A 82 85
B 75 81
[讨论]B 本题条件不全, 请参考10.24第15题的条件。


15. 一个表格，两个学校分别有a个人和b个人， median分别是85和75，mean分别是78和82，问两校合并后的median和mean那个大？
1）a+b=79 2）a=36，b=43
答案：E。这道题目大家都讨论很久了。
[确认] E

sunnY_yueliu

5。9. DS：一个数列，平均数与和的比
（1）共有8个数
（2）和为100
确认C

Why not A?

lisaislisa

Total number Mean  Median
I            82      85
II           79      78
Question: the mean of both II and I is larger than the median of both II and I?
A: I+II=89
B: I=42, II=37
--------------
from B; the mean of the total number is about 80
and since the media of I=42 is 85 it means20 ppl's scores are less than 85
since the media of II=37 is 78 it means 19 ppl's scores are less than 78
as polling together the score of 39th stu in this group is btw 78 and 85 ...
and since the mean 80 is also within this range , we still can't argue which is bigger , mean or media
is that the correct way for such problem ?

thx ^^

to yueliu
I agree with you ^^

lisaislisa

2.An insurance company has a paper record and an electronic record for every claim. For an inaccurate paper record, 60% chances that the electronic record is inaccurate. For an inaccurate electronic record, 75% chances that the paper record is inaccurate. 3% of all the claims are inaccurate both in paper record and in electronic record. Pick one claim randomly, what are the chances that it is both accurate in paper record and in electronic record?
A.97% B.94% C.68% D.65% E.35%
【确定】B 94%,
explain from David0822
For an inaccurate paper record, 60% chances that the electronic record is inaccurate.
x * 60% = 3% x = 5% (inaccurate paper record)
For an inaccurate electronic record, 75% chances that the paper record is inaccurate.
y * 75% = 3% y = 4% (inaccurate electronic record)
=> 2% inaccurate paper record, accurate electronic record
=> 1% inaccurate electronic record, accurate paper record
inaccurate paper record + inaccurate electronic record = 6%
ans:94%
----------------------------------------------------------
but I am afraid I will be dizzy dealing with the real test...
so can I think though this way ...
in 100 claim that is inaccurate in paper record , 60 are also inaccurate in electronic record
in 100 claim that is inaccurate in electronice record , 75 are also inaccurate in paper record
and in these 200 claims, 6 are both inaccrate in paper and electronic records ...
so ....but my idea block here ...can not go on ..and also not sure if it is the way out..
.


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margland

机警总结 12.27 机警总结 12.27 Robert之家数学JJ总结[附解题思路] http://www.topway.org Math总结本周值周斑竹:margland 本站原创,未经授权，严禁传统媒体转载，网络转载请注明来源 1.DS 三角形的三个外角x, y, z, how much is x? A: y=x B: z=x 确认C 2. 有8个人重量平均值是140磅，后来加入两个人重量平均值是143磅。 重量为正整数，问后加入的两个人中体重大的人的重量至少为？ 确认: 156 3，interview plan to interview 6 residents of 9 residents in the school, how many different combination of 6 out of 9? 这题我不太理解，是我的第四题，答案有15，..,84,2XX,504。我拿不到满分应该就是这一题丢的分。 思路：c(6,9)=84 4。一直线于两线相交得两角Y 和2X-5（在图上有表示），问Y= ？ 1） X=某数 2） 两线平形 确认：C 5。9. DS：一个数列，平均数与和的比 （1）共有8个数 （2）和为100 确认 A 6。K=0.1-(0.1)^2,问x>0.05(或,0.05) (1)K>0.009/X; (2)K<0.0009/X 确认：B 7。一圆园心在(1, -3)，圆在x轴上截得长度为8，求圆周长。 确认10pi 8. 一个花篮中的红花和白花数目之比是否为4：1 A 从花篮中任意抽出一朵花，抽出红花的概率为0.8 B 红花有60支 确认A 9、红花紫花的题，A和B两个篮子各有红花和紫花35，25；10，30。求从任意一个蓝子里抽出的花是红的概率。(数字改了，但答案没变) 参看robert 答疑45/(35+45+10+30) 10、75%的学生选生物，65%的学生选地理，求两门都选的最小值 确认：0.4 11.8个人，包括K、A， 从中选4个，有A但无K的概率 确认：2/7 思路：c(3,6)/C(4,8)=2/7 [em27][em21]

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