Tasty proportions

Last night, we did a fun activity in Math for Elementary Teachers at IUSB. We applied the concept of proportions to make our own trail mix. We knew the price of the whole container. As we put each ingredient into the bag, we had to check what a serving size was and compare that to the amount we used. When we were done, we had to figure out the cost of each ingredient using the appropriate formula. We added the cost of all the ingredients plus the cost of the baggie. My recipe included plain M&Ms, dried cherries, Honey Nut Cheerios, sunflower seeds, honey roasted peanuts, and pretzels. The final cost was $2.30. My total was quite a bit higher than some who skipped the M&Ms ($.67 for 2 servings) and dried cheeries ($1.14 for 1 serving). As I write, I am finishing off my yummy bag of goodies. I enjoyed this creative way to learn proportions but I am wondering how it could be done fairly and efficiently in an elementary classroom. I guess I can blaze that trail when I get there.