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  • How many strings of length 10 constructed from characters in the set {a, b, c, d, e, f} contain at least one a?

    A counting problem that I am having trouble solving. this is prb wrong, but my effort is this:

    Set up slots.

    _ _ _ _ _ _ _ _ _ _ (length 10). There are 6 strings in the set, but 'a' appears at least once in the string of length 10. So:

    6^5 + 6^5 + 6^5 + 6^5 + 6^5 + 6^5 + 6^5 + 6^5 + 6^5 + 6^6 = 132,192 strings with 'a' appearing at least once.

    approach maybe correct??? I would only like explanations or advice on how to approach it. No need to write everything out. I like to figure stuff on my own when I receive the necessary advice. Thank you!

    any advice will be appreciated.

    2 AnswersMathematics8 years ago