$5, $10, $25 Cash Cards

Have you noticed on some of the General Mills boxes that you could win a Discover Cash card with a value of $5, $10, or $25 dollars. These boxes hit Smith's first and about a five weeks ago, I actually had a box with a $25 card in it. I had bought several more boxes at Smith's but realized that someone there knew how to pick the winning boxes, most of the boxes there had been open as well. So stopped getting the cereal there. Today I went into Albertson's to use some soon to expire coupons in combination with the spend $25 get $10 back Catalina promotion currently going on. They have stacks of Trix that have not been tampered with so I did buy 30 boxes of Trix and found two $5 cards in the bunch. I love bonuses! The box states that 1 in every ten boxes has a card. This isn't gambling is it? I kind of have the urge to buy more just to see if I can get another $25 card. Ha ha