Thank you for the opportunity to help you with your question!
We have to make 3 choices, right? : the 2nd letter, the 3rd letter and
the 4th letter. Each choice is independent, so we multiply them.
Number of choices for 2nd letter x Number of choices for 3rd letter x
Number of choices for 4th letter
Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 21st, 2015
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