Did you ever notice how many different types of paper towels they have for sale in the market? It’s not bad enough that there are like 5 different brands, but within each brand there are different types: printed, quilted, “choose a size,” and let’s not forget single ply versus double ply. When you figure that you’ll probably go through one of these rolls each week (maybe even more, if your family is anything like mine) and then year in year out, it’s going to be a lot of money!
So I decided to collect some data about the prices of one brand of paper towels, because comparing two different brand is ridiculous: they all brag that theirs is better than yours, and it just gets so vomitrocious to figure out who is telling the truth and who has their pants on fire. These are the prices for the 9 different varieties of Bounty that are sold in different sized packs at a variety of discount stores around the country. Much thanks to Karrie of HappyMoneySaver.com for doing the dirty deed of collecting all this data. I would never have the patience to do such a thing....
What I did was put together an activity where students process all the information to make different kinds of “unit prices.” That’s because a “unit” can be almost anything, depending on what you want it to be. In this case, the “unit” appears as the price per roll of paper towels (because many are sold in “convenience packs,” which are only convenient if you own a home the size of Buckingham Palace....)
But a unit can also be the sheets per roll of towels, the number of square inches per sheet, the price for each sheet and the price per square foot of the roll. I would also try weighing the different rolls so that we can price them according to the price per ounce, because I’m going to bet that the actual paper in the different rolls has different weights. But let’s not go there, okay?
My 6th graders had a great time doing this activity, especially because I had them use calculators, which made things simpler in doing the computation, but they still had to figure out what was the best way to round off the numbers. If they rounded to the nearest penny, then they had a lot of prices that seemed the same, so they tried the hundredth of a penny (which would take them out 4 decimal places) and realized that gave them too much information. They then realized that tenth of a penny would work out fine.
One of the things you should definitely look out for is how they calculated the number of square foot in a roll. If you find the area of one sheet and then multiply that by the number of sheets, you’ll end up with square inches per roll. The question that your students should ask is this: how many square inches are there in a square foot? You can give them a clue by having them sketch a 12” x 12” sheet and ask how many square inches would be found inside: 12 x 12 = 144 square inches, so to go from square inches to square feet, you have to divide by 144. Fun!
Many of my students were indignant that a company would make so many different varieties of paper towels, and we talked about how it is somewhat of a miracle that our society has so many kinds of paper towels, but hasn’t figured out how to cure poverty, disease or end war. Go figure.