Could anyone advise me how to prove the following using combinatorial proof?
$$r\left(\begin{array}{c}n\\ r\end{array}\right)= n\left(\begin{array}{c}n-1\\ r-1\end{array}\right), r \geq 1$$
Hints will suffice, thank you.
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Expand combinatorial symbols in terms of factorials. Identity is immediate. – herb steinberg Aug 20 '19 at 17:15
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Thank you for the advice, but that is not what I am asking for. – Alexy Vincenzo Aug 20 '19 at 17:16
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What are you looking for? – herb steinberg Aug 20 '19 at 23:55
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Suppose you have to choose a group of r people from n people and then choose a leader for that group. this would give you a hint. – Amirhossein Aug 22 '19 at 14:31