求助 GWD29- 17, 32

m1225ark

17.

In a box of 12 pens, a total of 3 are defective.  If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?

 

A.     1/6

B.     2/9

C.    6/11

D.  9/16

E.    3/4

Answer:

c

  32. In the decimal representation of x, where 0 < x < 1, is the tenths digit of x nonzero?

(1)       16x is an integer.

(2)       8x is an integer.

                  

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.

Answer: B

請各位大大幫忙一下

anf

confused about Q17 as well

huangruiyan

以下是引用m1225ark在2008-9-3 12:04:00的发言：
17.

In a box of 12 pens, a total of 3 are defective.  If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?

 

 

 

 

 

 

 

A.     1/6

B.     2/9

C.    6/11

D.  9/16

E.    3/4

Answer:

c

  32. In the decimal representation of x, where 0 < x < 1, is the tenths digit of x nonzero?

(1)       16x is an integer.

(2)       8x is an integer.

                  

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.

Answer: B

請各位大大幫忙一下

17 ： 9个defective , 3个pefect  , .任选两个的可能性为 C2,12 . 人选两个neither defective  的可能性为C2, 9 . 则比例 为6/11

                                                 or    9 /12* 8/11= 6/11

概念： 从N个不同元素中人去M个元素组成一组 是组合概念，可以用Cm , n 表示

         如果题目是项目独立事件 ，比如问的是分别取出两个neither defective 的比率则是9/12* 9/12= 9/16

     32 : 16X =M  M 大于零的整数 ，X =M/16  已知 0< M/16< 1 M 有很多可能性，M最小 =1 , M 也可以等于8 ,那么X=M /16 就可以等于0.0625 or 0.25 十分位可以是0 也可以是非0 不充分

8X= M  M 是整数 ，X =M/8 已知 0< M/8< 1  M最小 =1 ,M/8=0.125 不管M去多少他的十分位永远不等于0

[此贴子已经被作者于2008-9-20 9:29:14编辑过]