You're right Toro, that IS the correct way to figure it, it's a rational gamble if the probability of winning times the size of the payout matches or betters the cost of a ticket. Except for the complication that there may be multiple winners, so even if you bought every possible set of numbers you could still lose. Actually with odds like these lotteries have, the probability of winning is pretty much the same whether you buy a ticket or not, for most practical purposes it's essentially zero, in the sense that you can't make plans on the assumption that you'll win something significant, but as others have rightly pointed out, it's cheap entertainment. I've never seen any stats on who buys tickets, but I'd bet it's mostly people in the lower half of the income distribution, and most of the activities that lotteries fund benefit the upper half of the income distribution. It's always seemed to me likely to be an income transfer from the poor to the wealthy.
