(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

By a combinatorial argument, prove that for r [tex]\leq[/tex] n and r [tex]\leq[/tex] m,

[tex](^{n+m}_{r})[/tex] = [tex](^{m}_{0})(^{n}_{r})[/tex] + [tex](^{m}_{1})(^{n}_{r-1})[/tex] + ... + [tex](^{m}_{r})(^{n}_{0})[/tex]

2. Relevant equations

3. The attempt at a solution

I need some direction on how to start this problem. It is the only homework problem I am not sure of how to approach it.

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# Homework Help: Probability proof by combinatorial argument

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