The multistate Powerball lottery jackpot has swelled to $365 million, the largest lottery jackpot ever in America. In 2001, mathematician Jordan Ellenberg explained why you're not a sucker for buying a ticket when the jackpot gets this big. "The question to ask is: What is the expected value of a lottery ticket? If the expected value is more than a dollar, and the ticket costs a dollar, you should buy a ticket. If the expected value is less than a dollar, you should keep your money."