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Math Help - discrete prob

  1. #1
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    discrete prob

    Hi
    Dopes somebody knows the answere for that kind of question?
    Determine the number of vectors(x1,...,xn) such that each xi is either 0 or 1 and sum(n,i=1)xi>=k
    Thank you
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  2. #2
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    Assuming that the value of n is fixed and 0 \le k \le n, then you are counting the number of bit-strings of length n that have the sum of their enters great than or equal to k. The bit-strings with k ones and (n-k) zeros fit that description. How may of those are there?
    Do it for each j, k \le j \le n.
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