# Math Help - Prove the identity using a combinatorial proof

1. ## Prove the identity using a combinatorial proof

Prove the identity

$\displaystyle \sum_{k=0}^{n} k {n \choose k} = n 2^{n-1}$

2. Uhm, what did you try to do?

3. I try to use a combinatorial proof that both side of the equation count the same thing.
Because I don't know how to try the equation, so I insert the image of it here. (785091c89b91773535544515523d773b.png)