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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- Jan 22nd 2007, 12:26 PMmauro21pldiscrete 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 - Jan 22nd 2007, 01:09 PMPlato
Assuming that the value of n is fixed and $\displaystyle 0 \le k \le n$, 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, $\displaystyle k \le j \le n.$