I was brushing my teeth. The next evening, after dropping my car off for a nail to be removed from the right rear tire, I killed time at Michaels and Trader Joe’s.

I created this lesson relative_ratios from that.

My 6th graders are working on ratios and proportions. I saw the three different-sized bottles of Listerine on my bathroom counter and thought, Hmmmm, what if I tell my kids that the smallest bottle has a volume of 1 cubic unit then let them guess the volume of the other two bottles.

Holy cow. I don’t know what people do with all this crafty stuff at Michaels, but the place has a ton of objects that come in different sizes! (Grocery stores are great too, but I ran out of time to take pictures and no longer wanted to be the creepy shopper.)

I stole a tape measure from the sewing corner of the store to measure the items’ various dimensions. Then I laid them out and took pictures. I expected the store manager to escort me out of the store, but nobody did. (I ended up buying the tape measure because memories of the Catholic nuns in Vietnam beating me with a stick still haunt me.)

Without the money to buy all these items to show my kids in class, I’ll just have to project their pictures on the big screen. (My kids should be getting better and better at estimation thanks to this website!) I can bring in my Listerine bottles!

So my plan is to show each set of items on the screen, explain to them what I mean by the first item having a volume of 1 cubic unit, and what it means for them to make estimates for the other items.

After they write down their estimates for the set, I give them the actual volume (or diameter) numbers to fill in. Then, using a calculator, they figure out the actual ratio for the set. [02/19: forget the calculators, I just gave them the numbers, lesson was not about them calculating anything anyway, just give the best estimates] Hopefully, by doing one set at a time, they get to hone in on their estimates for the next set and get better. Then I give out cash to the kids with best estimates.

Here is the answer key.

I like this lesson because the kids don’t have to worry about units or formulas. They just get to practice with comparing two things and so a lot of estimation along the way.

But the best lesson ever for ratios, of course, is this little known gem right here.

I plan to wrap up the lesson by showing them these toy models. Then maybe we can take a field-trip to the parking lot to walk around my car.

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