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There are 292.2 million total combinations in Powerball. The lottery sold 440.2

ID: 3124267 • Letter: T

Question

There are 292.2 million total combinations in Powerball. The lottery sold 440.2 million tickets last drawing.

Let us make a mathematical model. We will number all the possible Powerball combinations by natural numbers 1 through N (for Powerball in its current form, N =292,201, 338). This way, we can think of the lottery as choosing a random number between 1 and N.

We will assume that the lottery tickets are filled out randomly-with a uniform distribution-and independently. Suppose that K tickets are sold. We will assume that K > N.

Question. What is the expected 'coverage" of the drawing in which K tickets are sold? In particular, for each number n between 1 and N, what is the probability that exactly n different combinations are chosen?

Explanation / Answer

Expected coverage = ticket solds per unique number = 440300000/292201338= 1.506
Probability of exactly n different combinations = KCn*(1/n)^k