请教一道CXD的数学题目

herr_chenhy

Are there exactly 3 distinct symbols used to create the code words in Language Q?

1)      The set of all code words in Language Q is the set of all possible distinct horizontal arrangements of one or more symbols, with no repetition.

2)      There are exactly 15 code words in language Q

看了书上的解释，还是不明白。。望高人指点~谢谢

herr_chenhy

明白了。谢谢！

yangzhongyan

第二题,题目已经明确说了不用管order了,所以用组合,而不是排列

herr_chenhy

A company that ships boxes to a total of 12 distribtuion centres uses color
Coding to identify each center. If either a single color or a pair of two different colors
Is chosen to represent each center and if each center is uniquely represented by that choice of one or two colors, what is the minimum number of colors needed for the ending? (Assume that the order of the colors in a pair does not matter.)

这边的答案用的是C为什么不用P呢？N+P（N，2）和N+C（N，2）区别再那里？？谢谢

sunnyfields

1)+2）全部无重复：3+P（3，2）+P（3，3）=15，选C啦

1）只是排列条件，2）给你个数，什么都不能说明。