Q18:
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%
选D
Q23:
The toll for crossing a certain bridge is $0.75 each crossing. Drivers who frequently use the bridge may instead purchase a sticker each month for $13.00 and then pay only $0.30 each crossing during that month. If a particular driver
will cross the bridge twice on each of x days next month and will not cross the bridge on any other day, what is the least value of x for which this driver can save money by using the sticker?
A. 14
B. 15
C. 16
D. 28
E. 29
选B
Q30:
From May 1 to May 30 in the same year, the balance in a checking account increased. What was the balance in the checking account on May 30 ?
(1) If, during this period of time, the increase in the balance in the checking account had been 12 percent, then the balance in the account on May 30 would have been $504.
(2) During this period of time, the increase in the balance in the checking account was 8 percent.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
选c
Can anyone tell me the reasons why these answers are correct
给MM点建议：
做完题后，优先看置顶讨论
置顶讨论没有的先搜索
以你的问题为例，用“GWD18"作关键词在MATH区搜索即可查到。
23。http://forum.chasedream.com/dispbbs.asp?BoardID=22&replyID=1351667&id=145898&skin=0
30。http://forum.chasedream.com/dispbbs.asp?BoardID=22&replyID=1351733&id=145908&skin=0
18。http://forum.chasedream.com/dispbbs.asp?BoardID=22&ID=145883&replyID=&skin=1
啊呀，怎么找了没有找到，现在知道了
多谢了
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