computers 这个单词，选5个字母排列。words are formed using the letters of

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computers 这个单词，选5个字母排列。words are formed using the letters of the word"computers".how many different 5letter words are possible if:
1）没有限制排（there are no restrictions）
2)有两个元音字母（2 vowels must be used）
3) 至少用2个元音字母（at least 2 vowels must be used）
4) 5个字母的词，由元音开始，由元音结束（the word begins and ends with a vowel）
5) 由元音开始或者友元音结束（the word begins or ends with a vowel）

computers中共有3个元音字母,6个辅音字母
1）没有限制排列.

2）有两个元音字母,可以先从3个元音字母中挑出2个,再从6个辅音字母中挑出3个,然后遍历这5个字母的所有排列.

3）至少用2个元音字母,可以把所有的排列数减去全是辅音的排列数和只有一个元音的排列数,其中只有一个元音的排列即先取出1个元音,再取出4个辅音,然后进行重排.

4）由元音开始,由元音结束,选取2个元音放在首位并且考虑顺序,然后在从剩下的7个字母中选出3个（元音辅音皆可）且考虑顺序.

5）由元音开始或者由元音结束.
由元音开始：选取一个元音放在词首,然后从剩余的8个字母中选取4个遍历各种排列；
由元音结束：选取一个元音放在词尾,然后从剩余的8个字母中选取4个遍历各种排列；
重复部分：那些由元音开始,由元音结束的排列因为既属于由元音开始,又属于由元音结束,因此被多计算了一次,需要减去.

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