提问！回答！

sxcream

Q9:

If an integer n is to be chosen at random from the integers 1 to 96, inclusive, what is the probability that n(n + 1)(n + 2) will be divisible by 8?

 

A.     1/4

B.     3/8

C.     1/2

D.     5/8

E.      3/4

答案是D。虽然做对了，但是用的方法不是很简便，请高人帮我指点迷津！

Q16:

What is the probability that a student randomly selected from a class of 60 students will be a male who has brown hair?

(1)     One-half of the students have brown hair.

(2)     One-third of the students are males.

这道题目我做的也是对的，答案是E。但是不知道我的思路有没有问题。我是这么想的：BROWN HAIR的是30个人，MALE是20个人。20个人有可能是完全独立于BROWN HAIR的30个人之外的，也就是也有可能BROWN hair的都是女生。

Q29:

The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998.  Was the annual rent collected by the corporation from the building more in 1999 than in 1997?

(1)     x > y   

(2)      xy/100< x – y

像这样子抽象的题目我就搞不清楚了。。。

暂时求教这么多。发现自己做数学的时候还是太大意了。很多题目没看清楚题干就解题了。哎，马上就要上战场了，应该要调整好心态。为自己，为战友们加油！

sxcream

自己给自己顶一下。以往这个时候都有很多NN的回复了。今天咋了。。。

owenwei

q9:

if n is even,n(n+1)(n+2) is divisible by 8 for sure, total 48 even numbers

if n is odd,n and n+2 are odd, n+1 must be divisible by 8, so n+1 must be 8k,(k=1 to12) total 12 numbers

total 60/96=5/8

q16

1 is not sufficient (no information regarding male)

2 is not sufficient (no information regarding hair)

1,2 together are notsufficient(no information regarding the overlap between 20 males and 30 hairs)

q29

a1997,a1998,a1999

100*a1998=(100+x)*a1997

100*a1999=(100-y)*a1998

question:a1999>a1997?

a1999=(100-y)*(100+x)/10000 * a1997

so the key to answer the question is to determine (100-y)*(100+x)/10000 >1?

<=> -100y+100x-xy>0?

<=> xy/100<x-y ?

2 is sufficient

1 is not(i.e.if x=20,y=18,1997">"1999; if x=6,y=4,1997"<"1999)

pc123

1.if n is even, then any n in the range form 1-96 could fit the requirement. The amount of this kind of n is 48

  if n is odd, then only n+1 is the multiple of 8 can it fits the requirement. The amount of this kind of n is 12 

  there are total 60 Ns that could meet the requirement. the answer is 60/96=5/8

2. Agree with LZ

3. if using R representing rent collected from this building, we could form the follow equations:

   R1998=(1+x%)R1997; R1999=(1-y%)R1998=(1-y%)(1+x%)R1997. Is R1997 bigger than R1999? We should compare 

   1 with (1-y%)(1+x%). Obviously, choice 1 is useless. So take 2 into consideration.

   (1-y%+x%-x%y%)-1=x%-y%-x%y%. Is x%-y%-x%y%>0? yes. accordingto choice 2, we could find this one is bigger than 0.

   So choose B

  

sxcream

谢谢楼上各位！！！

zhang200824

这个事9月机经的提么？