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请教大家两道题

1.Amy's grade was the 90th percentile of the 80 grades for her class.  Of the 100 grades from another class, 19 were higher than Amy's, and the rest were lower.  If no other grade was the same as Amy's grade, then Amy's grade was what percentile of the grades of the two classes combined?

 

(A) 72nd

(B) 80th

(C) 81st

(D) 85th

(E) 92nd

请详细讲一下 percentile 这个词的理解,谢谢!

 

2.An automobile manufacturer offers a station wagon with either a 6-cylinder engine or a 4-cylinder engine and with either a manual transmission or an automatic transmission. A trailer hitch is also offered, but only on a station wagon with a 6-cylinder engine. How many combinations of the five options listed does the manufacturer offer for its station wagon?

 

(A) 3

(B) 4

(C) 5

(D) 6

(E) 8

请您更正或指点我的理解,谢谢! 我的理解是:题意中是不是隐含着6-cylinder engine 可以不带 trailer hitch? 如果是的话,本题中有三个分类:(1)station wagon with either a 6-cylinder engine or a 4-cylinder engine  (2) with either a manual transmission or an automatic transmission (3)就是带 trailer hitch 的6-cylinder 车和不带 trailer hitch 的6-cylinder 车

 

3.

70, 75, 80, 85, 90, 105, 105, 130, 130, 130

The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

 

 

(A) One

(B) Two

(C) Three

(D) Four

(E) Five

请帮忙详细讲解一下 rounded to the nearest tenth of a second 这句话。我的疑问是这句话到底是理解为:精确到十分之一秒即小数点后一位还是理解为:将最近的十分之一秒调整为整数,即按照四舍五入的原则,此处约等于22 seconds? 

 

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谢谢你的讲解,不过:

1.第一题是不是这么算 -- 90%*80=72 这说明在 Amy‘s class 有8个人排她前面,加上另一个班排她前面的19人是27人,再用27除以两班总人数180=15% 即意味着答案是85th?

这种就是这么算还是我的思路笨还有更简单的算法么?

2.本题我拿到的版本是选D 即6种方式,我自己也是这么选的,但是我选的前提就是我提问的那种分类,因为刚刚开始做GMAT数学所以对于题目没有提及的条件,我就自作主张按照隐含条件处理,不知这样对不对?

3.对于round ... 这个条件的理解当然不影响题意,但是就因为我是新手才想着把所有的条件,每一个单词的意思都搞懂,才问出了这个蠢问题。不过,对于 round sth up/down to sth 这个固定用法还是得留心啊...

再次致谢!

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第一题的pencentile的就和gmat的成绩单上的是一个含义啊,比方说你某项成绩的percentile是90%,就相当与说有89个人的成绩比你低,十个人的成绩比你高。知道这个后本题很简单,选85

第二题我也不太明白他是怎么分类的,答案是什么?


第三题 rounded to the nearest tenth of a second 的含义就是将数据精确到小数点后一位,对这个问题的理解不影响解题吧?答案是2个

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