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Math Help - Functions, Domain & Range

  1. #1
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    Functions, Domain & Range

    Let "A" be an n-element set and let k E N. How many functions f : A --> {0,1} are the for which there are exactly k elements in "A" with f(a)=1 ?

    Note: E = "be a member of" (k E N)
    N = Natural numbers
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  2. #2
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    If k>n the answer is 0.
    If 1\le k \le n then the answer is \binom{n}{k}.
    You may think of the number of ways to arrange k 1's and (n-k) 0's.
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  3. #3
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    Thank you Plato!
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