ChaseDream

标题: 请问GMATPrep 的数学题目 [打印本页]
作者: zhongzhiyu    时间: 2006-3-15 06:46
标题: 请问GMATPrep 的数学题目

1.     if 5^21 * 4^11=2*10^n, what is the value of n?
        A,11, b, 21, c 22, d,23 e 32


这种题目应该怎么去做呀。。看上去好容易，可是我忘记怎么去approach它了。。好像是有什么规则是不是呢？


2.    if n and m are positive integers, what is the remainder when 3^(4n+2) is divided by 10?


       1. n=2,


       2. m=1... answer is B, but why??


3.   A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?


     A, 3/40000, B 1/3600, C. 9/2000, D, 1/60, E, 1/15


我的排列组合不是很好，有没有哪位可以教教我怎么做呀？？

作者: zhongzhiyu    时间: 2006-3-15 06:55

在问一道题目


                   r        s      t


on the number line shown, is zero halfway between r and s?


1. s is to the right of zero


2. the distance between t and r is the same as the distance between t and -s.


作者: zhongzhiyu    时间: 2006-3-15 07:36

在问一道题目


                   r        s      t


on the number line shown, is zero halfway between r and s?


1. s is to the right of zero


2. the distance between t and r is the same as the distance between t and -s.


作者: hitlzc    时间: 2006-3-15 08:54

1.     if 5^21 * 4^11=2*10^n, what is the value of n?
        A,11, b, 21, c 22, d,23 e 32
这种题目应该怎么去做呀。。看上去好容易，可是我忘记怎么去approach它了。。好像是有什么规则是不是呢？


把 5^21 * 4^11表示成2*10^n的形式,5^21 * 4^11＝5^21 * 2^22=2*10^21,所以n=21,选b


2.    if n and m are positive integers, what is the remainder when 3^(4n+2) is divided by 10?
       1. n=2,
       2. m=1... answer is B, but why??


这道题有过讨论，我个人认为是有点bug


http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=152616&page=1


http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=160101&page=2


3.   A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
     A, 3/40000, B 1/3600, C. 9/2000, D, 1/60, E, 1/15


(60/1000)*(60/800)=9/2000 错误，请看6楼


4.                r        s      t
on the number line shown, is zero halfway between r and s?
1. s is to the right of zero
2. the distance between t and r is the same as the distance between t and -s.


已知t>s>r,问：s=-r(s>0)?,


1)s>0


2)|t-r|=|t-(-s)|=|t+s|,当s>=0时，s=-r；当s<0时，s=r-2t


所以选选C


[此贴子已经被作者于2006-3-15 9:42:34编辑过]
作者: zhongzhiyu    时间: 2006-3-15 09:18

3.   A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
     A, 3/40000, B 1/3600, C. 9/2000, D, 1/60, E, 1/15


(60/1000)*(60/800)=9/2000



答案是A,


好早哟你。。真的是非常感谢你的帮助

作者: hitlzc    时间: 2006-3-15 09:42
以下是引用zhongzhiyu在2006-3-15 9:18:00的发言：


3.   A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
     A, 3/40000, B 1/3600, C. 9/2000, D, 1/60, E, 1/15


(60/1000)*(60/800)=9/2000




答案是A,


好早哟你。。真的是非常感谢你的帮助


哦，对，是我搞错了，忽略了在一个年级里选了一个学生之后，另一个年级别无选择，只有一个人才是先选的这个人的sibling pair。

所以应该是(60/1000)*(1/800)=3*40000

作者: charlemagne    时间: 2006-4-3 13:12

不好意思。。。


60/1000  是什么意思呢？

作者: hitlzc    时间: 2006-4-3 14:52
以下是引用charlemagne在2006-4-3 13:12:00的发言：

不好意思。。。


60/1000  是什么意思呢？


是从junior class中随机抽出一人是sibling pair之一的概率。


[此贴子已经被作者于2006-4-3 14:52:49编辑过]
作者: leeup866    时间: 2006-11-29 20:39

还是不明白。

不是两个年级各选一人配对吗？那不是60/1000*60./800

作者: 期待蔚蓝    时间: 2007-1-2 12:39
同问！
作者: 期待蔚蓝    时间: 2007-1-4 01:23
作者: wuyi369    时间: 2007-1-4 05:39
这个问题要分开来看。。先从一个班里选择，那么随便选一个年级1000人里有60个人可以选择。。60/1000 概率。。 但是当你选好了一个人的时候，在另外那个班级里只有一个人士他的兄弟或者姐妹。于是1/800   。。。。不知道解释得是否清楚。。。当然 60/800 和  1/1000 的选择也一样可以
作者: tjk879    时间: 2007-3-3 00:07
4. r s t
on the number line shown, is zero halfway between r and s?
1. s is to the right of zero
2. the distance between t and r is the same as the distance between t and -s.

已知t>s>r,问：s=-r(s>0)?,

1)s>0

2)|t-r|=|t-(-s)|=|t+s|,当s>=0时，s=-r；当s<0时，s=r-2t

所以选C

各位XDJM,偶不明白"当s<0时，s=r-2t"是如何得来的?恳请哪位大虾指点,先谢了.





欢迎光临 ChaseDream (https://forum.chasedream.com/) Powered by Discuz! X3.3