mean and expectation

Question

when deciding which tire bill narrowed down to 20 inch, 22 inch, 24 inch, or 28 inch wheel. The prob of each being .35, .3, .15, .2 respectively 

 

Answer 1

E(x) = ∑x*P(x)  

       = 20*(.35) + 22*(.3) + 24*(.15) + 28*(.2)  

       = 7 + 6.6 + 3.6 + 5.6  

       = 22.8 inches