There are 9 tennis balls in a box, of which only 5 have not previously been used. Four of the balls are randomly chosen from the box. Let ⇠ be the number of new balls among the selected ones.

Question

There are 9 tennis balls in a box, of which only 5 have not previously been used. Four of the balls are randomly chosen from the box. Let ⇠ be the number of new balls among the selected ones.
(b) Evaluate the expectation E