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How many 3-letter words can we make from the letters A, B, C, and D, if we are allowed to repeat letters, and we must use the letters A and B at least once?

 Nov 17, 2020
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Possibilities

 

ABA  = Choose any one of three positions for  B  = 3

ABB  = Choose any  one of three positions for A  = 3

ABC  =   3!  ways to arrange this =  6

ABD =    3! ways to arrange this = 6 

 

 

18 possible "words"

 

 

cool cool cool

 Nov 17, 2020

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