A question about the a simple linear regression model

For a simple linear regression model, it is true that $\sum_{i=1}^{n}\frac{\hat y_i}{n}=\bar y$ but i am not sure how to prove it. It seems trivial but i want to know about the proof.

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Can you proveide some definitions for your terms? What is $\hat y_i, n$ and $\bar y$? –  Jeremy Oct 11 '12 at 4:19
Do you mean that the mean of the predicted ys is equal to the mean of the observed ys? –  Bitwise Oct 11 '12 at 4:35