Suppose I have a bag with 12 slips of paper in it. Some of the slips have a 2 on them, and the rest have a 7 on them. If the expected value of the number shown on a slip randomly drawn from the bag is 3.25 , then how many slips have a 2?
3a + 18 ==39,
[3a + 18] / 12==3.25, solve for a
There are: 9 twos and 3 sevens
x = number of 2's
12-x = number of 7's
[2 *x + 7 (12-x)] / 12 = 3.25
2x -7x + 84 = 39
-5x = -45
x = 9
