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Hello!!

I cannot figure out how to derive a closed formula for the sum of "the firsts" binomial coefficients:

[tex]\sum_{k=0}^{s} \left({{n}\atop{k}}\right)[/tex]

with [tex]s<n[/tex]

Could you please help me find out some trick to derive the formula... I've an exam on monday!!

Thank you very much!!!

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# Help: sum of binomial coefficents

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