There have been a few rare situations where playing the lottery was actually extremely +EV, mostly new games that come out when they aren't smart enough to figure out the math right away. The one that sticks in my mind was a medium sized lottery, maybe 100,000 numbers, in South Carolina I think. They came up with basically a normal lottery, but they had an additional bowl with 6 white balls and 1 red ball. If they drew the red ball, then the payout was doubled. But every time they drew one of the extra balls, they wouldn't replace it for the whole week. At one point only the red ball was left so it was a guaranteed double payout. A bunch of people that could actually do math went out and bought all the tickets they could and cleaned up. The lottery crew abandoned the promotion soon after.

Lee

Maybe I got the amounts wrong but I have read articles about groups of people buying all the tickets and making a profit on the cash payout.

Typically you have to match six numbers. If no one wins, the jackpot carries over. The jackpot is split among all winning tickets.