> whenever there's a rolldown, all tickets are positive EV, regardless of the number of tickets bought This is probably likely, but wrong in general. If the ti

> whenever there's a rolldown, all tickets are positive EV, regardless of the number of tickets bought This is probably likely, but wrong in general. If the tickets cost $1 and the total prize money is composed from e.g. 50% of the ticket prices plus a fixed amount of leftover prize money, when enough tickets are bought for the rolldown round, the leftover prize money isn't enough to cover for the 50% of the new tickets that doesn't go in the pot. Example: $2m leftover money in the pot, 5 million tickets bought for $1 each. EV = $2m + 50% of $5m = $0.9 per ticket. Now, if you buy enough tickets to guarantee e.g. 4 correct numbers and know for a fact that due to a rolldown the minimum payout is going to be high enough to cover the cost of that (at least with a high probability), then you're fine. I'd assume that's what the couple in the story did.