6月份数学鸡精总结 Update to Jun23 10:00 p.m.

instantreply

Q46: (Lu: This question maintains a water-tight logic!)

The probability that event A will not occur is 0.8.  The probability that event B will not occur is 0.6.  The probability that neither event A nor event B will not occur is 0.  What is the probability that one of the two events of event A and event B will occur?

Answer Choices: 2/5, 3/5, 12/25 …

Answer: 3/5

Note from Lu:

From “The probability that neither event A nor event B will not occur is 0.” → Neither A nor B will occur = 0.4 → This guarantees that “A Occurs” and “B Occurs” are two completely separate sets that have no overlapping area.   

Historical Question #1: (Lu: this question is not tested in the current cycle and it is only for your practice!)

What is the probability that event E or event F or both will occur?

(1)       The probability that event E will occur is 0.6.

(2)       The probability that event F will occur is 0.4.

Answer: E

Note:  This question is very misleading and tricky.  This question is actually testing the knowledge of Sets.  The two events may be dependent with each other or independent with each other.  If the two events are independent with each other, then the highest probability is 0.4 + 0.6 = 1 when the two events do not overlap; the lowest probability is 0.6 when 0.4 event is contained completely in the 0.6 event.

This edition is new in this month.  It is a DS transformation for an earlier PS edition that is famous for its novelty.  Check it out as below!

Historical Question #2: (Lu: this question is not tested in the current cycle and it is only for your practice!) (Moving Sets)

If the probability is 0.54 that Stock A will increase in value during the next month and the probability is 0.68 that Stock B will increase in value during the next month, what is the greatest possible value for the probability that neither of these two events will occur?

0.22

0.32

0.37

0.46

0.63

Answer: B

[此贴子已经被作者于2009-6-16 20:58:08编辑过]

upas

vivian0331说的那道题的解法，我同意

upas

关于59题，

A interrior decorator will paint the apartment , there are six colors of the painting the decorator can use:red, blue , green , yellow,white,and pink. how many choices the decorator can make with the white color included ever chice.

 

bigur解答: 说实话，题目真的看不懂什么意思。大体猜测一下，就是6种颜色可以和白色来混合，说有几种结果。那就是从6中颜色中，可以随便0-6种，有多少个取法

1+C(6,1)+C(6,2)+C(6,3)+C(6,4)+C(6,5)+C(6,6)= 64

是不是应该；5选1呢，而不是6选1.

另外关于83题，

83.说一共400人，戴手表的340人，带手机的80人，即带手机有戴手表的人是，既不带手机和既不带手表人数的一半，问有多少人带了手表没带手机（大致是这个意思）

Miaomiao:设：两个都戴的是X。 340+80-X=400-2X    算出来怎么X等于-20？

JJ里说X成了负数，不过是不是应该这样：

340＋80-X＝400－X*1/2 ，算出来X＝40 ，也就是说既带手表又戴手机的是40人，所以带了手表而没有带手机的是300人。

请大家讨论，NN指点

[此贴子已经被作者于2009-6-16 18:39:07编辑过]

upas

关于85题，

85. 480人其中音乐家占25%，15%的人是音乐家没参加会议，问参加会议的音乐家人数。

Miaomiao: 求既参见会议又是音乐家的人数： 480*0.25=120    480*0.15=72     120-72=48

是不是题干有点小问题，如果题目是JJ里给出的那样，那直接就是求480的10％了，也许15％是指音乐家人数中的15％（而不是全体人数的15％）没有参加会议，所以问参加的音乐家人数是120×85％。不想了，到时再仔细看题目是怎么说的吧

[此贴子已经被作者于2009-6-16 18:39:45编辑过]

upas

关于86题，

86. 还有一道ds，七个包裹已知总重量求中数，给出最轻四个的总重和后四个的平均重。

JJ里没有给出答案，我觉得是不是该选C？盼讨论

[此贴子已经被作者于2009-6-16 18:40:27编辑过]

upas

关于86题，JJ里没有给出答案，我觉得是不是该选C？盼讨论

妖舞夜魅

以下是引用upas在2009-6-16 18:08:00的发言：
关于86题，JJ里没有给出答案，我觉得是不是该选C？盼讨论

同意啊

妖舞夜魅

LZ你快回来啊啊啊

hang13

以下是引用upas在2009-6-16 18:08:00的发言：

关于86题，

86. 还有一道ds，七个包裹已知总重量求中数，给出最轻四个的总重和后四个的平均重。

JJ里没有给出答案，我觉得是不是该选C？盼讨论

86题 举一个反例就可以了

前4个和是8， 后4个平均值为3，即是和为12

2 2 2 2 3 3 4
1 2 2 3 3 3 3

所以根据目前给的条件，选E

amygreenrain

以下是引用instantreply在2009-6-16 17:13:00的发言：

Q46: (Lu: This question maintains a water-tight logic!)

The probability that event A will not occur is 0.8.  The probability that event B will not occur is 0.6.  The probability that neither event A nor event B will not occur is 0.  What is the probability that one of the two events of event A and event B will occur?

Answer Choices: 2/5, 3/5, 12/25 …

Answer: 3/5

Note from Lu:

From “The probability that neither event A nor event B will not occur is 0.” → Neither A nor B will occur = 0.4 → This guarantees that “A Occurs” and “B Occurs” are two completely separate sets that have no overlapping area.   

The probability that neither event A nor event B will not occur is 0.” → Neither A nor B will occur = 0.4

请问下这个怎么来的啊？？不明白。。

[此贴子已经被作者于2009-6-16 21:30:32编辑过]