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You have to give some to get some. That’s apparently the theory behind 7-Eleven’s campaign to dole out free Slurpees to customers on Monday to celebrate the chain’s unofficial birthday: 7/11.

USA Today reports that 7-Eleven expects to give out 5 million, 7.11-ounce Slurpees, or about 1,000 free drinks per store. No coupon needed.

That’s a lot of Slurpees, to be sure. But the paper says that 7-Eleven has found freebies to be very lucrative. The chain’s vice president of marketing Nancy Smith tells USA Today that the same gimmick last July 11 pushed Slurpee sales for the day up 33 percent.

"Slurpee drinkers are some of the most loyal fans we have," Smith told USA Today. "They come here to have fun." And, she said, many of them spend more on other items.

Thus proving there’s no such thing as a free lunch … uh, Slurpee.