Give a combinatorial proof
33104
Combinatorial Proof with Summation Identity
97254
What is the proof of permutations of similar objects?
71797
Combinatorial argument for $\sum\limits_{k=i}^{n}\binom{n}{k}\binom{k}{i} = \binom{n}{i}2^{n-i}$
56828
A combinatorial proof that the alternating sum of binomial coefficients is zero
35168
How to use combinatorial proof instead of induction?
61483
Prove the following identity combinatorially
156566
Combinatorial proof of a binomial identity: $\sum_k \binom {2r} {2k-1}\binom{k-1}{s-1} = 2^{2r-2s+1}\binom{2r-s}{s-1}$
150281
Am I on the right track to figure out this combinatorics problem?
74887
Combinatorial proof of the identity ${n+1\choose k+1}={k\choose k}+{k+1\choose k}+...+{n-1\choose k}+{n\choose k}$
44484
Combinatorial identity $i{n \choose i } =n {n-1 \choose i - 1}$
103504
Weird $3^n$ in an identity to be combinatorially proved
107964
Simple combinatorics problem.
116356
Combinatorial proof of $2 \cdot 3^0 + 2 \cdot 3^1 + 2 \cdot 3^2 + \cdots 2 \cdot 3^{n-1} = 3^n-1$
24212
proving how many permutations exist.
30136
Proof that a Combination is an integer
74523
Proof by Cases involving divisibility
117775
Combinatorial proof of a Stirling number identity.