Monday, January 30, 2017

7.RP.1, or Why the Math We Teach Might Actually Matter

Earlier today I read an article from the Atlantic about the financial insecurity of the US population.  (OK, I read three-quarters of an article before I was distracted by dinner preparation!)  I started to think about my friends, my coworkers, and eventually my students.  How many of them are living with virtually no financial safety net?

Because I work in a relatively poor area, my suspicion is that the 47% quoted in the article is actually an underestimate for my community.  And while that worries me for my generation, I think about what we need to do differently for young people so they can find themselves in a better situation a decade or so from now when they are established adults.

Recently, Maryland instituted a new graduation requirement: a course in financial literacy.  It's a good first step, though there are certainly growing pains with the new course.  I'm encouraged to hear that students learn about credit scores and responsible use of credit in the class.  I hope that they take to heart the lessons and consider how each decision they make can impact their future.

I was blessed to grow up in a household where we were comfortable and yet also one in which my parents didn't lavish me with things or encourage wasteful spending.  I've always had a thrifty way of approaching most expenditures, but not everyone has that kind of training.  I've gotten into money-saving apps and coupons in the past year or two (though I'm not an extreme coupon lady by any means) and I'm learning to stretch my dollar even further because it can actually be fun! 

Yesterday, I was standing in the paper towel aisle in Walmart surveying my choices.  I hate buying paper towels.  I simply don't find it possible to mentally price compare in the store and I end up just buying a huge pack of Bounty, my favorite anyway, knowing that I'm probably getting a crummy deal but that because I bought a huge pack I won't have to deal with the problem again for months.  Nevertheless, that extra little bit of wasted money irritates me.  A lot.

Here's what I'm talking about.  These screen shots are from various sites but have the same quality paper towel in packs for about $16.

Bounty at Target. 12 "mega" rolls.  Regularly $19.79, on sale for $15.99.  Buy two, get a $5 gift card. 


Bounty at Amazon. 12 "giant" rolls. $16.60 plus shipping.


Bounty at Menards. 6 "huge" rolls. $15.67


These three packs cost within a dollar of each other (ignoring for the moment shipping or incentives).  So, which should the consumer choose? 

The Amazon pack has the most rolls (12), and conventional wisdom says it's cheaper to buy in bulk. 
The Target pack has the equivalent of 20 regular rolls, which is the most of any pack.  The gift card inventive is also intriguing.
The Menards pack has the largest rolls with the most paper towels each.  That seems like a good deal, plus it means less paper towel tube waste and less need to change rolls. 

OK, I'm not really thinking too much about those things when I'm buying paper towels.  I'm trying to compare which rolls and which brands will give me the most for my money.  But even comparing among this one brand is tricky. 

I've been in stores where the shelf price tags that give a unit price are equally obtuse.  Some brands will have cost listed by sheet where others will have it listed by roll.  Even sheet-size is different; some brands have full size sheets and others have half-size sheets.  That's not easy to compare. 

Back to just Bounty, assuming this "regular roll" to be a standard unit of measurement, it looks like a regular roll at each store would cost:
Target: $15.99/20 =  $0.80 (or 26.98/40 = $0.67 if you factor in the gift card)
Amazon: $16.60/18 = $0.92 (before shipping)
Menards: $15.67/15 = $1.04

Standing in Walmart last night, I was armed with a $1.00 off coupon for a multipack of 6 or more rolls and a $2 ibotta rebate (sign up here to join ibotta and earn cash back on groceries- it's great).  I chose this pack of 6 super rolls for $8.98. 

Net cost after coupon and rebate was $5.98.  Price per roll $5.98/11 = $0.54.  (Even without coupons, at $0.81 per roll, this was a good buy in comparison to the field.)

Walmart's webpage started to make clear why this is such an exercise in proportional reasoning (or throwing your hands up in the air) with this helpful chart.  It turns out that a regular roll is a standard unit of measure for Bounty.  They make not just 3 or 4 but 10 different sizes of rolls! 



So, now I feel vindicated and like I won the game that is paper towel shopping.  Next time your students want to know when they'll ever use 7.RP.1 in real life, you can tell them about how much fun it is to shop for paper towels.  Or just take them on a field trip to the big box store and ask them to get the best price! 

Small comparison shopping tasks like this one, repeated over time, can help us become more financially secure.  Throwing up our hands and taking the path of least resistance means that we're using our resources for something we might not prioritize.  If we can help our students learn these lessons early, perhaps they will be better off than our generation and our parents' generation. 

Mathematically yours,
Miss B



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