Normally I do not get that excited about grocery shopping, but this Sunday was an exception: I used OR to do my grocery shopping.

Many grocery stores have promotions that encourage shoppers to buy 10 items, such as the 10 for $10 sales. Oddly, there has typically been no penalty for buying fewer than ten items: all items would be $1 each. The sale merely suggests to stock up on ten or more sale items.

This past year, my favorite grocery store (Kroger) has periodically offered a promotion that offers $5 cash back for every ten items purchased (but not any ten items, just the items associated with the promotion). The items range in price from $0.99 to $5.99 before the discount. The promotion essentially offers an a savings of $0.50 per item, which is 50% off of an item costing $0.99. But no problem so far; I just partition my wish list into groups of ten and stock up on extra rice cakes until a reach a multiple of ten. [Check out the ad]

There is an additional twist this week: a combinatorial challenge. Most of the items in the promotion have coupons in the Sunday paper that require the purchase of two or three items. For example, I had two coupons for $1 off of three boxes of Kleenex. The Kleenex are on sale for $1.49 (not the best sale), would be effectively $0.99 after the promotion (not too shabby), and would be $0.66 after the coupon (a bargain!). But I can only buy them at this price if I buy three or six boxes. Maybe this isn’t exciting to you, but my kids went through two boxes of Kleenex this week when they had the sniffles.

On Sunday morning, I cut out coupons and made a list of promotion items my family could use. I made sure that (1) the total number of items on my list was a multiple of ten, (2) individual items were purchased in groups of two or three (according to the coupon restrictions), and (3) individual items were within the lower and upper bounds according to our needs (there are only so many cartons of orange juice we can drink).

I bought 30 items with the promotion, saving $15 with the promotion and an additional $12.30 with coupons. I even found some bargain-priced day old bakery bread. Needless to say, it was the most fun I have ever had at the grocery store. Kroger has a good OR team, and I appreciate some of the savings–and challenges–they offer shoppers.

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Have you ever had a combinatorial shopping experience?