A lottery official says the estimated prize for this weekend's Powerball drawing has grown to about $800 million, making it the largest jackpot of any lottery game in U.S. history.

No one has won the Powerball jackpot since early November, which is why the prize has grown so large. The bigger prize entices more people to buy tickets, and that drives up the jackpot.

The increased ticket sales also make it more likely there will be a winner, simply because all those extra tickets mean more number combinations are covered. Scott A. Norris, an assistant professor of mathematics at Southern Methodist University, said there's no trick to playing the lottery, but your tiny odds of winning are a bit better if you let the computer pick rather than choosing yourself. That's because when people use birthdates or other favorite figures, they generally choose numbers 31 or below. That ignores the fact that there are 69 numbered balls.

Your odds increase with additional tickets, but it's important to keep in mind how small they are to begin with. If you have a 1 in 292.2 million chance of winning with one ticket, you have 10 times the odds if you buy 10 tickets. Yet the probability is still incredibly small. "The odds are so astronomically small that even 100 times that number is exceedingly unlikely to win," Norris said. "It's probably still not going to happen if you buy a hundred tickets or a thousand tickets or even a million tickets."

If you have extra cash and are thinking of buying all possible number combinations, that is allowed, but it wouldn't be very smart. At $2 a ticket, the strategy would cost about $584 million, and when taxes are subtracted, you'd end up losing money. And if someone else had the winning numbers, you'd need to split the prize. You'd make back some of that money by smaller prizes paid for matching three, four or five of the balls plus the Powerball, but chances are it still wouldn't be a good bet.