Rounding Decimals: Microwave Madness and a Microwave Mystery

Subjects
4th, 5th, 6th, 7th
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1.15 MB   |   8 pages

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A lot of people ask me where I get all the ideas for my materials, which, you’ll have to admit, are rather strange in many ways. When you see math “everywhere” like I do, you’re always thinking about how math “fits in.” I came home from work one day in the mood to make gungjung tteokbokki, and wouldn’t you know, all I had was frozen pork. So I pulled it out of the freezer and stuck it in the microwave on the “defrost” setting (which actually works pretty well.) What I noticed was that I had purchased 1.17 pounds of pork, but the microwave only lets you put in weight to the nearest tenth of a pound. So I had to round it off to 1.2 pounds, which worked just fine: after all, does adding 3/100 of a pound to the defrost time really affect things? You guessed it.

So that’s the inspiration. But it also got me thinking this: if I put in 1.2 pounds, I could have purchased lots of different weights of pork, because you almost never see exactly 1.20 pounds of anything: scales these days read out to the nearest hundredth of a pound and print it on the labels, which I guess is good for the stores, since it reassures customers they’re paying for exactly what they’re getting, and not .001. pound more or less. If I needed 1.2 pounds, then 1.15, 1.16, 1.17, 1.18, 1.9 pounds all would have rounded off to 1.2, as well as 1.21, 1.22, 1.23 and 1.24. But not 1.25, which would round off to 1.3 pounds.

Anyway, I tried this out on my students and they really had fun with it. Many of them went home and checked their microwaves and found out that indeed, they only cook weights to the nearest tenth of a pound, while everything sold in the supermarket is measured to the nearest hundredth of a pound. Ain’t math great? That's how the "riddle" works.

I hope you check out the rest of my materials in my store; believe me, they’re not like anything else you’ve ever seen.
Total Pages
8
Included
Teaching Duration
45 Minutes

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