The lottery is a game of chance in which players pay for tickets, select numbers or have machines randomly spit them out and hope to win prizes. Most states and the District of Columbia have lotteries, and people spend an estimated $70 billion a year on them, reports the Huffington Post. Lotteries are considered a form of gambling, though many of the people who play them don’t consider it gambling at all. They think of it as a fun way to spend money, and they don’t feel that the games are regressive.

But the system isn’t foolproof. For example, if you choose numbers such as birthdays or ages that hundreds of other people also pick (e.g., 1-2-3-4-5-6), you’re less likely to win than if you picked random numbers, Harvard statistics professor Mark Glickman says. And if you win a prize, you’ll have to split it with all the other people who have your chosen number or sequence.

In colonial America, lotteries were a popular way for private institutions to raise money. They were used to help fund colleges, canals, bridges, roads and even military fortifications. Some of the nation’s most elite universities, including Columbia and Princeton, owe their start to lotteries.

Today, lotteries are still a major source of revenue for state governments. The big jackpots, which attract national attention and drive ticket sales, have become a mainstay of the games. But the underlying system is not foolproof, and some people use strategies to increase their chances of winning.