求NN，问几道prep数学，5/28，急急急

kevinh1217 · 发表于 2013-5-25 14:53:40

5/28 考，今天摸了一下，好多题不会做啊，求NN们指点，谢谢了

The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present. If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A  100% decrease
B. 50% decrease
C.  40% decrease
D.  40% increase
E. 50% increase

-------------------------------------------------------
Tanya prepared 4 different letters to be sent to 4 different addresses . For each letter, she prepared an envelope with its correct address. If the 4 letters are to be put into the 4 envelopes at random. What is the probability that only 1 letter will be put into the envelope with its correct address?

A  1/24
B  1/8
C  1/4
D  1/3
E  3/8

--------------------------------------
What is the greatest prime factor of 4^17-2^28

A 2
B 3
C 5
D 7
E 11

------------------------------------------------------------------
What is the remainder when the positive integer n is divided by the positive integer K, where K > 1 ?

1.  n=(k+1)^3
2.  k=5

----------------------------------------------------------------------------

A certain city with a population of 132,000 is to be divided into 11 voting districts , and no district is to have a population that is more than 10 percent greater than the population of any other district. What is the minimum possible population that the least populated district could have?

A  10700
B  10800
C 10900
D 11000
E  11100

----------------------------------------------------------------------

hohohohoho · 发表于 2013-5-25 15:49:40

有些内容不好编辑，见谅
1 正比于 a平方/b b为2b a平方要变为两倍a平方 a为根号2a = 1.4142 所以是 40% increase
2 设四信封为 A B C D 四信件 a b c d 任意放置全排列 4x3x2x1 = 24种

hohohohoho · 发表于 2013-5-25 15:56:54

2继续只有一封对了  设为a 剩下2情况 :  a c b d or a d b c 所以有4x2=8种答案为1/3
3  2^34-2^28 = 2^28 x 63  答案： 7
4  (k+1)^3 =  k x (k+1)^2 + (k+1)^2  展开后面余数为1
5  不太好解释  设最小为a  其余10个为1.1a  所以 a + 1.1a x 10 = 12a = 132000 答案为 11000
不知道正确与否  仅供参考

kevinh1217 · 发表于 2013-5-25 16:27:48

hohohohoho 发表于 2013-5-25 15:56
2继续只有一封对了设为a 剩下2情况 : a c b d or a d b c 所以有4x2=8种答案为1/3
3 2^3 ...

谢谢大神，太给力了！！

kevinh1217 · 发表于 2013-5-25 16:29:30

hohohohoho 发表于 2013-5-25 15:56
2继续只有一封对了设为a 剩下2情况 : a c b d or a d b c 所以有4x2=8种答案为1/3
3 2^3 ...

谢谢！明白了，要求最小的是多少，让另外10个最大就可以了，range不能超过10% 是这样吧

hohohohoho · 发表于 2013-5-25 16:34:51

额。。。有点难解释。。。这么想吧。。。假设11个都一样就是平均值12000，这时候选中其中一个12000使其变小，同时另外 10个12000 就要变大，才能使总值不变。。。最后的结果就是 a 和 10个1.1a 当然你可能问为什么不让10个变小而一个变大，这就会走向另外一种情况！！！所以你仔细想一下，应该可以明白！

hohohohoho · 发表于 2013-5-25 16:38:35

如果实在不行，可以用排除法，直接带入 10900，去极限情况，另外10个为10900 x 1.1 x 10 为 119900 这样达不到 132000... 然后代入11000 可以！

kevinh1217 · 发表于 2013-5-25 21:07:16

hohohohoho 发表于 2013-5-25 16:38
如果实在不行，可以用排除法，直接带入 10900，去极限情况，另外10个为10900 x 1.1 x 10 为 119900 这 ...

给力了！多谢 ^^

求NN，问几道prep数学，5/28，急急急

所属分类: GMAT考试

正在浏览此版块的会员 ()

浏览过的版块