Doctor-approved backpack weight?
I came to our lesson on linear inequalities in two variables, which coincidentally closely follows our discussions on direct variation, scatter plots, and linear regression. I wanted to find a unique real-world application for the lesson that tied these two topics together. 

I found a blog post for the New York Times wellness section that gave a decent path HERE: the relationship between student body weight and their backpack weight. The American Academy of Pediatrics recommends the student's backpack "never weigh more than 10 to 20 percent of your child's body weight." Consumer Reports insists that a backpack weigh no more than 10% of the student's body weight (I feel it necessary to point out that the emphasis of their claim seemed to be focused on elementary school-aged students; their insistence seemed to loosen up on secondary students, citing that their back muscles are stronger at those ages and better fit for a bit more extreme load).

So, enter the lesson, sans the lab coats and clipboards that the Consumer Reports folks might have access to, and determine: 
Are my students' backpacks in compliance with the most extreme of these doctor recommendations?

I've created several activities that are intended to accompany this activity. Here are some of them:
  • TI-Nspire CX activity [If you do not have TI-Nspire Teacher Software to open this file, download the file first, then use the TI-Nspire Document Player to view it without need for purchase or download] The activity will walk students through analyzing their class's data (NOTE: The teacher should note the slideshow at the bottom of this post for pointers as to how this activity is set up. Student weights are "hidden" on the first/title page of this document), as well as a couple of final Self-Check questions to conclude the lesson with a check for understanding.
  • GeoGebraTube post for the graph and spreadsheet to display a class's data, showing the Compliant and Non-Compliant regions as they pertain to doctors' recommendations regarding this weight relationship.

Please note the slide show below for images of each of these activity resources with captions to help give pointers as to the intent of the activities as well as user tips and tricks.
Some helpful tips on successfully executing this lesson:
  • Don't forget to use an accurate scale! I was able to call in a favor with our school's wrestling coach and use their official scale since this lesson happened to fall during their off-season. Especially helpful--since some students were bashful about their data being seen by others--was the fact that the scale had a detachable display screen which could be faced away from their peers.
  • Yes, I indulged a bit when using the TI-Nspire CX's (especially since we actually were able to use the CAS version of them). They work great this early in the school year to grab students' attention and quickly engage them in a topic like this one. I otherwise would use a similar activity using the TI-84s we have access to.
  • I do not mean to play down the power of GeoGebra in this post. It is a very visual tool and my students have enjoyed it in many other lessons, but it was dependent on me having contained my lesson within a separate file, in this case a PowerPoint. No big deal, but with a couple of network snafus among one of my larger class sizes, I revised last year's lesson plan to instead use the TI-Nspires this time around.

As for the photo at the left of my backpack and the banner above my classroom window (both KELTY, by no coincidence): there's no real rhyme or reason, I just wanted to give a shout out to the company. I still have students who believe I faked both products so that I could dub myself with a pretty sweet nickname.

Well, who's laughing when my endorsement deal with them rolls in? Right? Hint, hint...

--Keltner-- I mean, Kelty