PREP+FF数学，裸奔在即，盼望NN救命！

GMATdeJULY

1.函数H（X）是1到X之间所有偶数乘积。文H（100）+1的最小质因子是落在哪个区域。

A2到10；B10到20；C20到30；D30到40；E40以上

答案E

2.DS题。each of the 25 balls in acertain box is either red, blue, or white and has a number from 1to 10 on it. if one ball is to be selected at random from the box, what is the probablitiy that the ball selected willeither be white or have an even number on it?

1.The probalbility that the ball will both be white and have an even number painted on it is 0

2.the probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2

第一个难道不可以独立解决了吗？。。不懂。。

3.DS。 if the operation"#"代表加减乘除中的1个，问（6#2）#4=6#（2#4）？

1.3#2大于3

2.3#1=3

我觉得交换律加法乘法都可以，就选了D。。

4.先给出12个数：7.51，8.22，7.86，8.36，8.09，7.83，8.30，8.01，7.73，8.25，7.96，8.53

a vending machine is designed to dispense 8 ounces of coffee into a cup. After a test that recorded the number of ounces of coffee in each of 1000cups dispensed by the vending machine, the 12 listed amounts, in ounces, were selected form the data(就是先前给的那12个数）if the 1000recorded amounts have a mean of 8.1 ounces and a standard deviation of 0.3 ounce, how many of the 12 listed amounts are within 1.5 standard deviations of the mean?

A.4;B 6;C9, D10, E11

题目问以上12个有多少个平均数的标准差再1.5之内，可是每个数的标准差等于X-X拔的绝对值，X拔是8.1，以上没有1个数和8.1相减绝对值能够有1.5的丫。。我TOTALLY不懂。。想法比较单纯

5.差不多的一道：The resident of Town Xparticipated in a survey to determine the numberof hounrs per week each resident spent watching television, the distribution of the resuts of the survey had a mean of 21hours and a standard deviation of 6hours. The number of hours that Pat, a resident of Town X, watched television last week was between 1and 2 standard deviations below the mean. 问PAT这个人上个星期可能看了多少小时的电视？

A。30，B20， C18， D12，E6

答案是D12.我选了B20，我的思路是PAT的标准差和平均数在1和2之间而且比平均数低，也就是平均数21去减掉PAT的时间在1和2之间.。。哪里错了望NN指正

6. At a certain university, the ratio of the number of teaching assistant to the number of students in any coure must always be greater than3:80. At this university, what is the maximum number of students possible in a course that has 5 teaching assistants?

不会做。。望NN指下思路。。

7.先给出了一张表:

Score interval        Number of Scores

   50-59                               2

   60-69                              10

   70-79                               16

   80-89                              27

   90-99                              18

问那个分数区间里contains the median of the 73 scores?

A.60-60,B.70-79,C80-89,D90-99 E.it cannot be determined from the information given

我选的E，答案是C。80-89

我的思路是如果存在中位数73也是应该在70-79这个区间里呀。。但是现有信息只给了70-79这个区间里有16个数，不能确定73一定是70-79这个区间的中位数啊，所以我选了E。答案出乎意料是C。。80-89区间里怎么会存在73是中位数呢？。。。完全不懂。。

8.DS题。在XY平面上，问直线L的Y截距。

1.L的斜率是Y截距的3倍

2.X轴上的截距是-1/3

答案是E。我选的C。俩个条件直接可以确定L的一次函数表达式啊。。为什么是E呢？？。

9. If the operation:#" is defined for all integers  a and b by a#b=a+b-ab, which of the following statements must be true for all integers a, b, and c？

I.a#b=b#a

II.a#0=a

III.(a#b)#c=a#(b#c)

答案好像是以上3个都行。不懂，望NN指点思路

10. When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a cinstant amount each year for the next 6 years. At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year.By how many feet did the height of the tree increase each year？

A. 3/10,B 2/5,C1/2,D.2/3,E6/5答案选D

我的思路是设每年恒定的增长数为F，那第6年是4+5F，第4年是4+3F。问题是“the tree was 1/5 taller than it was at the end of the 4th year”这句话怎么理解？

是（4+3F）×（1+1/5)=4+5F呢，还是 4/5×（４＋５Ｆ）＝４＋３Ｆ？还是4+3F+1/5=4+5F？

无论是哪个式子算出来都没有题目给的选项。。迷茫。。

11. DS题。During a one day sale, a store sold each sweater of a certain type for $30 more than the store's cost to purchase each sweater. How many of these sweaters were sold during the sale?

1.During the sale, the total revenue from the sale of these sweaters was $270

2.During the sale, the store sold each of these sweaters at a price that was 50 percent greater than the store's cost to purchase each sweater

答案是C，我选的A。REVENUE不就是卖价-买价=30？总REVENUE是270，卖的个数就是9个啊。。。错哪儿了，望NN指正。

wy88sunny

25 balls
each one is red, white, or blue
each one has a number from 1 to 10

Want: white OR even (note that we DON'T want white AND even - we have to be able to strip out those that fall into both categories). To calculate, can either do:
a) probability of "white and odd" + probability of "even and not white"
b) probability of white + probability of even - probability of white & even

(1) Translated, this means there aren't any that are both white and even. This doesn't tell us how many are white or how many are even. Insufficient. Eliminate A and D.

(2) Pwhite - Peven = 0.2. So, Pwhite could be 0.4 which would make Peven 0.2. Or Pwhite could be 0.3 which would make Peven 0.1. And (by itself) it doesn't tell me Prob of even & white, which I'd need to subtract, so... insufficient in many ways. Eliminate B.

(1) AND (2) Now I know that Peven+white = 0. BUT, I still have multiple possibilities for Pwhite and Peven (see above). 0.4+0.2-0=0.6. 0.3+0.1-0=0.4. ?? Still insufficient.

wy88sunny

可以百度GOOGLE,我上面就是百度的，哈哈

GMATdeJULY

强。。你百度的我正在研究。。

must700

纠正一下你上面几个标准差问题的理解错误。

1.5 standard deviations means 1.5*standard deviation 并不是the deviation is 1.5

在4题中是1.5*0.3

GMATdeJULY

嗷明白！

昨晚刚看过你答给另外1个同学提出的标准差问题，这个问题已经明白了！THX MUST700 NN！

GMATdeJULY

7.先给出了一张表:

Score interval        Number of Scores

   50-59                               2

   60-69                              10

   70-79                               16

   80-89                              27

   90-99                              18

问那个分数区间里contains the median of the 73 scores?

A.60-60,B.70-79,C80-89,D90-99 E.it cannot be determined from the information given

我选的E，答案是C。80-89

这个是怎么回事？

konell

做中数题先要排序，不过此题已经排好序了，就直接找73/2=36.5,也就是第36，37位在哪个分数档了——所以C

daisy1980626

2的答案应该是E吧，不太同意楼上的说法，解释如下：

求球是白或偶的概率，应该包括同时满足白和偶。。。

1说同时是白和偶的概率为零。不能给出是白或偶的概率。。。

2说是白的-偶数的概率为0.2，也不可以

1和2的话，由1，P白或偶=P白+P偶，但是第二个条件没有进一步给出P白+P偶的概率，反而给了P白-P偶的概率，所以不能得到结果。

因此选E.

麻烦告诉我一下正确答案，让我印证一下啊。

daisy1980626

3的答案应该是C吧，注意是数据充分性的题目，在选项满足的情况下，可以求得题目中的问题。。。由2得可能是乘或除，再加上1，知道是乘，这样才可以计算出原题。