GWD-23-30/20-36/18-QX

GWD-23-Q30

There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.  How many possible selections of 4 books from this self include at least one paperback?

A. 40
B. 45
C. 50
D. 55
E. 60
答案选C，我怎么做都是D，C84-C64=55,大家帮我看看

GWD-20-36

Q36:
If a and b are positive integers such that a – b and   are both even integers, which of the following must be an odd integer?

A.a/2 
B.b/2
C.(a+b)/2
D.(a+2)/2
E.(b+2)/2
答案是D，我不会做

GWD-18-QX

QX:
If the probability is 0.54 that Stock A will increase in value during the next month and the probability is 0.68 that Stock B will increase in value during the next month, what is the greatest possible value for the probability that neither of these two events will occur?

A. 0.22
B. 0.32
C. 0.37
D. 0.46
E. 0.63
答案是B
设stock A not increase的概率是P(A)=0.46，stock B not increase的概率是P(B)=0.32，则，原题中neither of these two events will occur的概率可以表示为P(AB)=P(A)+P(B)-P(A+B)=0.78-P(A+B)，但是因为P(A+B)不知道，我算不出来答案

请教NN们解答！！

第三题，你先算Ａ不涨的概率是０．４６，　Ｂ不涨的概率是０．３２．　两个同时发生，画个图，就可以知道，他们交集的范围是０＜Ｘ＜＝０．３２，　所以选Ｂ啊，不用真的要算出来．　

对对对，最小是０啊，脑子晕了啊　

前两题....up下~！

第一题，我也算55

第二题，题目好像缺了点东西啊 such that a – b and ？are both even integers

# GWD-23-Q30

答案错，正确答案是D

# GWD-20-36

http://forum.chasedream.com/dispbbs.asp?BoardID=22&ID=175872&replyID=1663565&skin=1

# 另外，请楼主以后发贴一题一问，以便后人查找

# 这次既然贴已发了，就麻烦楼主自己把标题改为：GWD-23-30/20-36/18-QX，行么？

方法：点击贴子右下角的“编辑”，修改完毕按“发表”即可。

# 以后做GWD题有疑问时，可先用搜索功能，很多题目前人已提过并有解决方法；如果真的搜索不到，再发贴上来问。

方法：如果GWD第3套Q5，则搜索的关键词：3-5

啊，了解了解，嘿嘿！！多谢大家的回答

sammy兄弟，多谢提醒，以后一定注意哈