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Math Help - Permutations without Repetition

  1. #1
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    Permutations without Repetition

    How many different numbers can be formed by taking one, two, three, and four digits from the digits 1, 2, 7, 8, if repetition are not allowed ?

    Please Help
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  2. #2
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    I just tried this again, and i got the answer 64, am I correct ???
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  3. #3
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    Quote Originally Posted by creatively12 View Post
    How many different numbers can be formed by taking one, two, three, and four digits from the digits 1, 2, 7, 8, if repetition are not allowed ?
    Using the notation _N\mathcal{P}_k=\frac{N!}{(N-k)!}
    the answer is \sum\limits_{k = 1}^4 {_4 \mathcal{P}_k } .
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  4. #4
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    Thanks for the reply

    so my answer is correct right ???
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