求教几题

lilyxiang910

1. If 10⁵⁰ – 74 is written as an integer in base 10 notation, what is the sum of the digits in that integer?

 

A.     424

B.     433

C.     440

D.     449

E.      467

                        Answer:  C

 

 

 

2.A certain club has 20 members.  What is the ratio of the member of 5-member committees that can be formed from the members of the club to the number of 4-member committees that can be formed from the members of the club?

 

A.     16 to 1

B.     15 to 1

C.     16 to 5

D.     15 to 6

E.      5 to 4

Answer:
                                    C

2.A certain club has 20 members.  What is the ratio of the member of 5-member committees that can be formed from the members of the club to the number of 4-member committees that can be formed from the members of the club?

 

A.     16 to 1

B.     15 to 1

C.     16 to 5

D.     15 to 6

E.      5 to 4

Answer:
                    C

 这两道题到底是怎么算的呢，看着答案还是算不出来，希望能帮我解答一下，谢谢！

 

 

 

 

 

 

 

 

 

rose0807

第二题，（20里随机取5）/（20里随机取4）=（（20!-15!)/5！）/((20!-16!)/4!)=16/5

Oia

第一题：

10^50 - 74 = 99999999999.....26

这些digit的和是 9*48+2+6=440

这道题的关键是理解：written as an integer in base 10 notation

不知道理解的对否。

第二题：

题干有点儿绕： C(5,20) / C(4, 20) = 16/5

[此贴子已经被作者于2009-1-21 15:31:42编辑过]

lilyxiang910

哦，原来是我把题目理解错了，多谢楼上两位了！