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Dr. Lizardo writes down a sequence of  letters, where each letter is A, B, or C, and the letter A appears an even number of times. How many different sequences could Dr. Lizardo have written down?

 Aug 4, 2020
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How long is the sequence?   Only 3 letters      ?   is  ZERO A's considered a possibility?

 

AAx

AxA

xAA      where x can be   B or C        3 x 2 = 6 sequences

 Aug 4, 2020

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