re: Cashier at store told me one guy has spent $4000 on Powerball

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My math could be wrong, because this thread is full of funky math, but I believe the probability of the QPs picking 2000 random numbers without repeating any of the same combinations is 99.317536%, so it is pretty safe to assume they were all unique.

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I actually envisioned it like the Birthday Problem LINKwhereas the probability is calculated by the total possible pairs.

Basically, if you randomly took 23 people, and asked what the probability that 2 of those individuals share a birthday, it may be intuitive to say 6.3% (23/365) but the true probability 50.7%. This is because we are looking at all possible pairs.

So if this is the correct way to look at it (which I believe it is), then there is roughly a little over 6% chance that you'll draw the same combination twice.