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Hello! My friend gave me this interesting problem and I can't figure it out. If anyone has any ideas it would be appreciated.

 

Problem: Liz writes down a sequence of \(n\) letters, where each letter is A, B, or C, and the letter A appears an even number of times. How many different sequences could Liz have written down?

 

The answer should be in terms of n. I tried to find a recursion and a closed formed but didn't have much luck.

 May 28, 2021
 #1
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Number  of   unique  sequences   =    number  of  words of  length  n  composed of  letters  A, B or  C 

 

                                 n !

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(occurences of A) ! * (occurences of B) ! * (occurences of C) !

 

 

 

cool cool cool

 May 29, 2021

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