菜菜鸟又上来求助啦！

sxcream

Q3:

If a committee of 3 people is to be selected from among 5 married couples so that the committee does not include two people who are married to each other, how many such committees are possible?

 

A.     20

B.     40

C.     50

D.     80

E.      120

这道题目我选的是E，因为是5*10+5*10+10+10.就是先从男的里面选一个女的里面选两个或相反，然后还有就是男的里面选三个或女的选三个。。。我觉得很正确呢，可是答案是D。

Q28:

Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day.  If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper B, which of the following expresses r in terms of p?

 

A.     100p / (125 – p)

B.     150p / (250 – p)

C.     300p / (375 – p)

D.     400p / (500 – p)

E.      500p / (625 – p)

题目本身的醒目的红色，应该是提醒这个的难度吧。事实上我也确实没做出来。请指教！

Q30:

Joanna bought only $0.15 stamps and $0.29 stamps.  How many $0.15 stamps did she buy?

(1)     She bought $4.40 worth of stamps.

(2)     She bought an equal number of $0.15 stamps and $0.29 stamps.

                  

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

这个我做了两遍了，一个次的答案是D。。这次的答案是A。。。可是我两次做的都是C。。。。难道。。。用穷举法？

frankmfg

For quesiton 3, the equation is
10C3-5C1X8C1=120-40=80

skin

最后一题答案好像是Ａ哦

首先２）肯定不充分

看１）

０．２９Ｘ＋０．１５Ｙ＝４．４

０．２９ｘ的末尾可以使任何数，而０．１５ｙ只能是５ｏｒ０

４．４０末尾是０

那么可能是两个都是０ｏｒ两个都是５

两个都是０的话即ｘｙ都是１０的倍数，只能是１０罗

两个都是５的话１．４５（０．２９＊５）ａ＋０．１５ｂ＝４．４

这样ａ可以取值１，２，３

其中取２时，有２ａ＝１０属于上面一种情况

取１，３是，ｂ不为整数，不存在

ｓｏ

只能是ｘｙ都等于１０　

skin

另外，第一题还想到一种解法，先从１０人里面随便选一人，然后除去选择的这个人和ＴＡ的爱人之后剩下的８人里面选一人，再从除去以上两对的６人里面选一人，即是１０＊８＊６＝４８０，由于选择的时候进行了排列，而题目显然只要求组合，除以Ａ３＝６，即４８０／６＝８０

这样可以不用考虑男男女女了，高中的时候好像就是这么做这种题的

dxh_1101928

我觉得第三题就是D呀，为什么2不行呢

sxcream

以下是引用frankmfg在2009/9/20 18:19:00的发言：
For quesiton 3, the equation is
10C3-5C1X8C1=120-40=80

理解了。

dxh_1101928

第2题the answer is D

Heres how:

Let the total newspaper sold be 100.

Newspaper A sold = p
Newspaper B sold = 100-p
Total revenue = p*1+(100-p)*1.25
So revenue from paper A = p*1 = p
Revenue percentage from paper A = (p/(p+(100-p)*1.25))*100
This is equal to r
thus
(p/(p+(100-p)*1.25))*100 = r

=> r = 100p/(125-0.25p)
Multiplying by 4 in numerator and denominator on RHS, we get
r = 400p/(500-p)

Hence the answer.

sxcream

以下是引用dxh_1101928在2009/9/21 18:17:00的发言：
第2题the answer is D

Heres how:

Let the total newspaper sold be 100.

Newspaper A sold = p
Newspaper B sold = 100-p
Total revenue = p*1+(100-p)*1.25
So revenue from paper A = p*1 = p
Revenue percentage from paper A = (p/(p+(100-p)*1.25))*100
This is equal to r
thus
(p/(p+(100-p)*1.25))*100 = r

=> r = 100p/(125-0.25p)
Multiplying by 4 in numerator and denominator on RHS, we get
r = 400p/(500-p)

Hence the answer.

Thanks!