Question

请教4道GMAT数学题，我要解释。。我不需要几个字母啊，谢谢

Q2:
A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?

A. 16%
B. 32%
C. 48%
D. 84%
E. 92%

Q24:

Factor Percent of Respondents
User-friendly 56%
Fast response time 48%
Bargain prices 42%

The table gives three factors to be considered when choosing an Internet service provider and the percent of the 1,200 respondents to a survey who cited that factor as important. If 30 percent of the respondents cited both “user-friendly” and “fast response time,” what is the maximum possible number of respondents who cited “bargain prices,” but neither “user-friendly” nor “fast response time?”

A. 312
B. 336
C. 360
D. 384
E. 420

Q28:
A school administrator will assign each student in a group of n students to one of m classrooms. If 3 < m < 13 < n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?
(1) It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.
(2) It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

Q35:
For what percent of those tested for a certain infection was the test accurate; that is, positive for those who had the infection and negative for those who did not have the infection?
(1) Of those who tested positive for the infection, did not have the infection.
(2) Of those tested for the infection, 90 percent tested negative.

Answer 1

我2.17也考GMAT。来回答你的问题哦：
Q2：题设说的是数据分布在均值附近一个标准差范围内的比率是68%。问：数据比均值+1个标准差这个数小的概率是多少？解答是1-(1-68%)/2=84% 选D
Q24：解答：选“user-friendly”或者“fast response time”或者两者都选的人数所占比率是56%+48%-30%=74% 所以选的是neither “user-friendly” nor “fast response time的人数所占比率是1-74%=26% 再乘以总人数 26%*1200=312 选A
Q28：把n个学生往m个教室里分，问是否有可能使得每个教室里的学生人数相等？如果(1)成立，假设n=14，则3n=42,m = 6 or 7,再回到原问题，把14人往7教室里放，每教室放2人即可 选(1)
Q35：感染的人是+，没感染的人是-。什么情况下能说明这个测试是准确的呢？(1)：显示+的人实际上并未感染。这个现象应该说明的是测试不准确，所以选（2）
祝LZ考试取得好成绩哦，也祝我自己，我们一起加油~~