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Math Help - Combinatorial and algebraic proof involving a permutation

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    Combinatorial and algebraic proof involving a permutation

    Hi guys, can anyone please tell me the combinatorial and algbraic proof of P(n+1, r) = P(n,r) + P(n,r-1)? Thanks for your help.
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    What are you even talking about?
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    Quote Originally Posted by cookiejar View Post
    Hi guys, can anyone please tell me the combinatorial proof of P(n+1, r) = P(n,r) + P(n,r-1)?
    That is not true of permutations. Let n=10~\&~r=4
    \mathcal{P}(n+1,r)=7920 while  \mathcal{P}(n,r)+\mathcal{P}(n,r-1)=5760

    Is true for combinations \mathcal{C}(n+1,r)= \mathcal{C}(n,r)+ \mathcal{C}(n,r-1) .
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