How Much Is A Ton Of Dollars?

NOTE: Apparently Chris Robinson already asked this question on and I totally missed it (or forgot).
Sorry, dude. Ma bad.

I rarely watch TV these days, but today I heard this commercial while watching a recording of Perception (“Silence” episode):

“If you had a dollar for every dollar car insurance companies say they’ll save you by switching, you’d have like a ton of dollars.”

Oh really? Interesting.

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Cheap Shrinky Dinks (for math or just cool to do with your kid)

I used to teach middle school and I LOVED it. Something about kids who haven’t hardened their hearts about math was just really cool. This was one of the things I used to do with my students and, since most of us are stir crazy at home with our kids, I figured you could try it out on them and see what you think. Originally got it from an AIMS article back in the 90’s.

Before you give me excuses about why you can’t do it, let me say:
If your kid is old enough to DRAW, then he/she is old enough to do some of this.
So at least try it.

So the first thing you need is PLASTIC and not just ANY plastic. It needs to be “Grade 6” plastic. I used to use the salad plates from the school cafeteria. I’d pay the cafeteria manager ahead of time for them (ridiculously cheap), and she’d order what I needed or give me what she had.

You’re looking for a recycle triangle with a “6” in it AND you need to make sure that the plastic is completely CLEAR (not foggy or anything). Here’s an example of what I’m talking about:

Notice that there is a “1” in there instead of a “6”. So I would NOT use this.

Once you get your plastic, just cut it up into whatever pieces you want. Here are the main supplies you’ll need:


  • plastic
  • sandpaper
  • pencil
  • ruler (if you want straight edges)
  • scissors
  • color pencils
  • hole punch (if you want to make it into a keychain, necklace, earrings, etc.)
  • a piece of paper (this is important)

Later you’ll need:

  • oven
  • spatula
  • tin foil

1. Go ahead and set your oven to 450 degrees. I’ve used toaster ovens in the past (about $20 from Wal-mart – VERY MUCH worth the cost if you’re doing this in your classroom) and I’m more familiar with that. Today’s the first time I ever tried it in an oven. It worked, but not as well as the toaster oven.

2. Take your sandpaper (cut into smaller squares), your first piece of plastic, and a piece of paper. SAND ON TOP OF THE PAPER. That piece of paper will keep you from sanding your desks, table, etc. (not that I’ve EVER done that before… *cough cough*)

3. Start sanding – we’re only going to do ONE side. Over the years, I’ve found a method for the madness. Sand your plastic top to bottom in one direction (ex: left and right). You gotta put your elbow into it, so don’t do this in a prissy manner. Imagine the face of someone you don’t like on that plastic and GO TO TOWN to scratch the crap out of it (not that I’ve ever done that before… *cough cough*). Then rotate the plastic so that your strokes are perpendicular to the ones you were doing before. Trust me, when you think you’re done, you’re NOT:

I can still see the clear plastic shine when I tilt it in the light. You’ve gotta make sure that sucker is completely sanded. It shouldn’t take that long, though. If you’ve spent more than 10 minutes sanding and it’s not finished, you’re not putting enough force into it. Once I’m sure that I’ve sanded every part of the plastic using those two strokes, I start sanding in a circle. This isn’t necessary, but if you look below, you can see that the difference between the perpendicular strokes (at the top) and the circular strokes (at the bottom). It’s easier for the color pencil to hold onto the plastic the better it’s sanded.

When you’re finished, it should look something like this:

Again, tilt your plastic in the light and see if it reflects. If it does, sand that part down. 4. If you’re doing this for math class or you’re just anal about it looking pretty (and I mean that in a non-judgemental sort of way), I use the notebook paper to help me line up my straight edges and I mark it in pencil:

5. Once that’s done, I cut it out. OPTIONAL: I always had my students trace the original on a piece of paper and measure it (I didn’t simplify one of the fractions, but if you wanna, go ahead – knock yourself out). I also made them do the diagonal, but that’s just an extension.

6. Now for the fun part. COLOR IT! I use color pencils. I haven’t tried markers (but I don’t really remember why right off the bat… oh well). I was in a hurry so I did this for my classroom keys:

NOTE: If you’re going to want to do this for a keychain or a necklace, punch a hole in your plastic BEFORE you cook it. I know that’s a “duh” thing, but afterwards you can’t do much about it so make sure you plan:

——-> Side note: after I baked it, I realized that one hole wasn’t big enough for the keychain I wanted to use. So for bigger keychains, be creative and make a slightly bigger hole.

7. So between me and the kid, we ended up with 2 each in about 15 minutes:

8. Now for the fun part! Transfer your plastic onto a cookie sheet COVERED IN ALUMINUM FOIL (you’ll thank me later).

See how they’re all spaced out? There’s a reason for that.

When they cook, they do this rolly-poly belly flop kind of thing and they, well, DANCE. Every time I do it, the dance is different. Some times it’s very fluid, and sometimes it’s really choppy. Sometimes they flip completely over, sometimes they roll completely up. Doesn’t matter, JUST WATCH. It is the coolest thing and kids will go CRAZY for it. You wanna make sure they have plenty of room to do their thing, though. If they “touch”, then those two pieces will probably bond together and you don’t want that. The cooking process doesn’t take long. I put the kid’s shrinky dinks in first to make sure the oven was at the right temperature. Here’s a video of mine going in (and YES, I burned myself – wouldn’t be ME if I didn’t):

9. When they come out, VOILA!! Mini-me’s!

Here’s the mini-version in the same rectangle as the original:

And in case you NEED to know, here are the measurements:

And here are the finished products:

It honestly took longer to blog about it than to do it. But you can do just about anything with this – gift labels, Christmas ornaments, keychain with your kid’s artwork on it, earrings, necklace, bracelet, etc. Be more creative than me. 🙂

One year my MathCounts crew set up a table for a fundraiser. Kids paid $1 to create one in assembly-line form OR up to $5 to have one custom made by our more artsy math nerds. We even mass created some with our school name in our school colors and sold those for $3. Just a thought.

I have the docs I used in my classes (7th grade math) SOMEWHERE around here, but it will take me a day or two to dig them up. Once I find them, I’ll post them. I used it to teach percent of change, but you could do just about anything with it. I suggest doing it as instruction and then again maybe the day after a state/standardized test as stress relief. Or maybe as a stats activity, you can have kids collect the data on the original and mini-me versions and see if they can create a regression equation to predict the length of the mini if given the length of the original piece. OR, even cooler, take that regression equation and have them use it in a “backwards” way. In other words, if they want the mini-version to be a specific length, what size original would they need?

If you DO this, I’d love for you to link to a picture in the comments or e-mail me (approximatelynormal dot stats at gmail dot com) and let me post it.

That’s all I’ve got for now, but I’m working on a post for mentor teachers with Chris Hill (@Hillby258) that should be ready today or tomorrow.

Until then….