How many combinations of three letters from the letters A,A,B,B,C,C,D are ther?(adsbygoogle = window.adsbygoogle || []).push({});

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I assumed 2 cases:

1. 2 letters are the same.

2. all the 3 are different.

And found 9 forms for the first case, and 24 for the second one. As you know my answer (33) is 20 more than what is written in the book.

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# Help with Combinations

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