[求助]求助ＮＮ一道ＰＲＥＰ的数学题～～

xin861123

39.   5583-!-item-!-187;#058&004668

A certain stock exchange designates each stock with a one-, two-, or three-letter code, where each letter is selected from the

26 letters of the alphabet.  If the letters may be repeated and if the same letters used in a different order constitute a different code, how many different stocks is it possible to uniquely designate with these codes?

 

(A)  2,951

(B)  8,125

(C)  15,600

(D)  16,302

(E)  18,278

算了很久还是没算出来~~~请求帮助下~~

ted810

算26^3+26^2+26的个位数为8。

题目中只有一个个位数是8，就选他。

xin861123

为什么这样算呢？对不起，太笨了～～没想通

xin861123

麻烦再求助一道题～～

50.   4230-!-item-!-187;#058&003784

A construction company was paid a total of $500,000 for a construction project.  The company's only costs for the project were for labor and materials.  Was the company's profit for the project greater than $150,000 ?

 

(1)  The company's total cost was three times its cost for materials.

 

(2)  The company's profit was greater than its cost for labor.

kevinling

题目很简单，就是考算术，要是有计算器就秒杀了

公式是=26+(26+P(2,26))+(26+C(2,26)*3+P(3,26))=18278

不要问我26怎么来的

我解释一下C(2,26)*3怎么回事:就是从26个字母里去2个字母，因为3letter code里面可能有2个字母是重复的，然后这样的排序由3种(xyy,yyx,yxy),所以C(2,26)*3

LZ应该懂了吧

kevinling

50.   4230-!-item-!-187;#058&003784

答案是C么?

题目条件:Total=50, C=L+M, 50-C>15?

1)C=3M, 则L=2M,50-3M,由于M不知道，不能确定
2)P>L, 则50-C=50-L-M>L, 仍不能确定50-C>15?
1)+2): 50-C=50-L-M>L=>50-3M>2M=>M<10, 则50-3M>20,能确定50-C>15了

JJever

题目很简单，就是考算术，要是有计算器就秒杀了

公式是=26+(26+P(2,26))+(26+C(2,26)*3+P(3,26))=18278

不要问我26怎么来的

我解释一下C(2,26)*3怎么回事:就是从26个字母里去2个字母，因为3letter code里面可能有2个字母是重复的，然后这样的排序由3种(xyy,yyx,yxy),所以C(2,26)*3

应该是C（2，26）×6吧，而不是3，应为选了2个数，还有种可能是xxy,xyx,yxx

对吗？

kevinling

应该是C（2，26）×3，怎么会*6？？

3个字母其中2个字母是重复的情况只有3种阿:xyy,yyx,yxy,为什么还要再乘2？不懂LS的意思