If you watch sports on television, you have probably seen ads for DraftKings, FanDuel and other gambling services.

More than 20 states and the District of Columbia have made betting on sports legal in the past couple of years. Americans spend billions of dollars annually on sports betting.

Although it is not legal for kids to bet on games, it’s a good time to talk about gambling. After all, kids see the ads, too.

An important thing to remember about gambling on sports is that the betting is designed so it is very difficult for the gambler to win. A gambler may win some bets, but over time most lose money.

Let’s look at one example — betting on a National Football League game.

Last Sunday, the Washington Football Team (WFT) played the Buffalo Bills. The “betting line” before the game was that the Bills were favored to beat the WFT by seven points. That means if a gambler bet on the Bills, the Bills had to win the game by more than seven points. The Bills beat the WFT by 22 points (43-21), so anyone who bet on the Bills won. The folks who bet on the WFT, however, lost money.

It’s important to realize that the betting line — seven points in the Buffalo/WFT game — is set so the games appear close and about half the gamblers bet on the Bills and the other half bet on the WFT.

A gambler usually has to give the betting service $11 for the chance to win $10 (the extra $1 goes to the service for handling the bet). If the gambler wins, he gets his $11 back and an additional $10. Sounds good, right? But if the gambler loses, he loses $11. Getting $10 if you win but losing $11 if you lose means over time most gamblers lose money, because it is hard to pick game winners more than half the time.

Let’s say a friend wanted to play a card game. You deal the cards face down, and you and your friend bet a nickel on who will have the higher card. If your friend has the higher card, she takes the two nickels. If you have the higher card, you win the money.

But your friend adds another rule. Every 10th time you flip over the cards, your friend wins the money even if you have the higher card.

Would you play that game? No way, the game isn’t fair. Just like betting on sports, the card game is designed so it is very hard for you to win.

Still, millions of people do something similar every day. They bet money on games and sports with betting services even though it is very hard for them to win. And some can’t stop gambling.

The ads make sports betting look like a fun and easy way to make money. But when you look closer, betting on sports is not smart.

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