问几个GMATPrep上的数学题

tiwwang

1， 9.4, 9.9, 9.9, 9.9, 10.0, 10.2, 10.2, 10.5

the mean and the standard deviation of the 8 numbers shown are 10 and 0.3, respectively. what persentage of the 8 number's are within 1 standard deviation?

A) 90% B) 85% C) 80% D) 75% E) 70%

答案是D， 请问这么做的， 我是no idea.

2. 一个公司， 800人， 70％服务10年以上， 如果这些人中有y个人退休， 也没新人加入； 那当y是多少的时候，可以使服务10年以上的人的比例为60％。

我： 80， 800×（70％－60％）

答案200, 请问为什么

3，if X=/=-y, is (x-y)/(x+y) >1? 1) x>0, 2) y<0.

我选C， 答案居然是E， 我很ft

zs8373

第一题,10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

2: let y=x, the number of people working more than 10 years=560

    (560-x)/(800-x)=60%  x=200

3 dont understand x=/=-y????

tiwwang

以下是引用zs8373在2005-12-27 6:11:00的发言：

第一题,10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

2: let y=x, the number of people working more than 10 years=560

    (560-x)/(800-x)=60%  x=200

3 dont understand x=/=-y???? x不等于y

前两题搞懂了， 谢了：）

tonywzj

如果X=2,Y=-3,那 (x-y)/(x+y) ＝5/-1=-5<1

所以答案为E

conquergmat

1， 9.4, 9.9, 9.9, 9.9, 10.0, 10.2, 10.2, 10.5

the mean and the standard deviation of the 8 numbers shown are 10 and 0.3, respectively. what persentage of the 8 number's are within 1 standard deviation?

A) 90% B) 85% C) 80% D) 75% E) 70%

答案是D

解题思路:10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

为啥蓝色部分能够说明standard deviation是1?

conquergmat

顶

hitlzc

以下是引用conquergmat在2006-5-14 0:35:00的发言：

1， 9.4, 9.9, 9.9, 9.9, 10.0, 10.2, 10.2, 10.5

the mean and the standard deviation of the 8 numbers shown are 10 and 0.3, respectively. what persentage of the 8 number's are within 1 standard deviation?

A) 90% B) 85% C) 80% D) 75% E) 70%

答案是D

解题思路:10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

为啥蓝色部分能够说明standard deviation是1?

题目不是说了 within 1 standard deviation吗。

catcenter

 within 1 standard deviation

汗,原来要表达的是这么个意思

现在做MATH都要求阅读能力了。..

我理解为标准差为1....

hitlzc

以下是引用catcenter在2006-5-25 20:11:00的发言：

 within 1 standard deviation

汗,原来要表达的是这么个意思

现在做MATH都要求阅读能力了。..

我理解为标准差为1....

MATH还真是要求阅读能力和逻辑能力。

有的数学题很简单，完全是在考察阅读和逻辑，大家多注意啊

carlzhou

解题思路:10-0.3=9.7 10+0.3=10.3 the number within 1 standard deviation should be between 9.7-10.3 so there are six numbers within 1 standard deviation 6/8=75%

6从哪里来的?这题还没转过弯来