A box contains five $1 bills, two $5 bills, and one $10 bill. If a person selects one bill at random, find the expected value of the draw.

I am really not sure how this works but I think

 

$$\left({\frac{{\mathtt{1}}}{{\mathtt{8}}}}{\mathtt{\,\times\,}}{\mathtt{10}}\right){\mathtt{\,\small\textbf+\,}}\left({\frac{{\mathtt{2}}}{{\mathtt{8}}}}{\mathtt{\,\times\,}}{\mathtt{5}}\right){\mathtt{\,\small\textbf+\,}}\left({\frac{{\mathtt{5}}}{{\mathtt{8}}}}{\mathtt{\,\times\,}}{\mathtt{1}}\right) = {\frac{{\mathtt{25}}}{{\mathtt{8}}}} = {\mathtt{3.125}}$$

 

So I think the expected value of the draw is      $3.125    or     $3.13    rounded of to the nearest cent.