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Combinations Problem

  1. Oct 14, 2005 #1
    I was thinking that I could solve this with combinations. However, I am unsure of how to use it in this case. If I remember correctly, the combinations are given by:

    [tex]\begin{pmatrix}n \\ r\end{pmatrix}=\frac{n!}{r!\,\left(n-r\right)!}[/tex]

    Hmm. Any thoughts on this? Am I on the right track with the above?

  2. jcsd
  3. Oct 14, 2005 #2


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    There are [itex]2^{10}[/itex] ways of selecting the digits and [itex] _{10}C_3[/itex] ways of having three 1's.
  4. Oct 14, 2005 #3
    Alright. I was thinking that it didn't matter if they were the same number; I could still use the formula above. Thanks for the confirmation :smile:.
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