PREP中三题，请教高手。。附答案

XIAOYUEHAN

166.

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

选B，看不懂，也不会做。。

3   A manufacturer produced x percent more video cameras in 1994 than in 1993 and y percent more video cameras in 1995 than in 1994.  If the manufacturer produced 1,000 video cameras in 1993, how many video cameras did the manufacturer produce in 1995 ?

1 xy=20

2 X+Y+XY/100=9.2

答案选B

请问2为什么可以求出？

4. Working alone at its own constant rate, a machine seals k cartons in 8 hours, and working alone at its own constant rate, a second machine seals k cartons in 4 hours.  If the two machines, each working at its own constant rate and for the same period of time, together sealed a certain number of cartons, what percent of the cartons were sealed by the machine working at the faster rate?

(A) 25%
(B)
(C) 50%
(D) 66*2/3%
(E) 75%

选D， 看不懂题目也不会解答

wumeier

第一题：

十个小孩儿跑400米所需时间分别是以上十个数，这十个时间的标准方差是22.4，精确到小数点后第一位。这十个数中，有几个数比这十个数的算术平均数小一个以上（more than one）标准方差（22.4）？

答案：两个，分别是70，75。求出算数平均数为100，then100-22.4=77.6，因为是more than one standard deviation，所以结果肯定该比77.6小，那就是前两个喽。

第二题：

（1+X%）x1000x（1+Y%)=一九九五年的产量=（1+X%+Y%+XY%%）x1000

                                      =1000+10x+10y+0.1xy

                                      =1000+92

                                      =1092

BruceNornia

... 我把第三个题目翻译一遍吧 我困惑的是  66*2/3%这个数字是什么意思

 

Working alone at its own constant rate, a machine seals k cartons in 8 hours, and working alone at its own constant rate, a second machine seals k cartons in 4 hours.  If the two machines, each working at its own constant rate and for the same period of time, together sealed a certain number of cartons, what percent of the cartons were sealed by the machine working at the faster rate?

 

当单独工作于其自身的稳定工作率时，某机器密封k个纸箱需8小时；同样当单独工作于自身的稳定的工作频率时，另一机器密封k个纸箱需4个小时。如果两台机器(每个都工作在与上述相同的工作率)一起密封一定数量的纸箱时，那么工作率较高的那台机器密封了百分之多少的纸箱？

 

这个题目其实很容易理解，题目的第一句话描述了两个机器其中一个的工作率为另一个的两倍

所以一起工作的话 必然其中快的那个密封的纸箱书为另一个的两倍 所以占总量的66%

XIAOYUEHAN

what percent of the cartons were sealed by the machine working at the faster rate? 这句啥意思，要求啥，我也当时算到V3=3K/8

yahooww

1,额..要找10个数中,在比MEAN小的数中,与MEAN的差比标准方差小的数...

只有70,75

2,X+Y+XY/100=9.2

看到这,我们准备求1+X/100)(1+Y/100)=1+x/100+y/100+xy/10000

到这,应该明白了吧..

3,V1=K/8

V2=K/4

面对K CARTONS

SET THE NEW ONE COST AS Y

1/Y=1/8+1/4

Y=8/3

V3=3K/8

额,后来看到问题,发现上面不要算的...随便写出来...权当偶的思路

问最快机器在相同时间内生产的产品在所有中的比率.

一看就知道.8小时,4小时.肯定是2/3的产品...所以是66.67%

BruceNornia

4 比较奇怪

 

自愧资质有限  难以领悟题目要旨

BruceNornia

3 1993的产量为 1000

1994的产量为  1000(1+y%)

1995的产量为  1000(1+y%)(1+x%) = 1000(1+x%+y%+x%y%)

 

如果知道 X+Y+XY/100=9.2 则 1+x%+y%+x%y% = 9.2%

从而 1000(1+x%+y%+x%y%) 可以计算

所以条件2 是可以的

BruceNornia

166 题目的意思：

70 75 80 85 90 105 105 130 130 130

上述列表所示为10个学生跑400米跑所用的时间。该10个数的标准差为22.4，四舍五入到10分位，有多少学生的跑步成绩比上述列表的平均数低出一个标准差以上？

平均数为： (70+75+80+85+90+105+105+130+130+130)/10 = 100

比平均数低1个标准差的数字 必须 小于 100 - 22.4 = 77.6

所有数字中 比77.6 小的只有 70和75 两个 所以B Tow