Rounding

Posted on November 18, 2016

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For some reason this was my ‘food for thought’ on the ride home yesterday.

Rounding is in that category of skills that is “really important for real life situations” — which students memorize convoluted rituals for getting right on their math homework. Things like “Find your number, move next door, Four or less, just ignore, Five or more, add one more.”

Why not get a little conversation going about precision?

I was thinking of grounding the lesson in familiar examples of the same units in different situations.  So — if I want to talk about how much a baby weighs, I’m going to want to be more precise than if I want to know what my backpack weighs, or what a truck weighs.

Here’s an interesting little challenge:  when, in life, do we actually round more precise numbers to bigger ones?   We estimate all the time, but how often do we consciously round?

With money, I think some of us round — but others punch things into that calculator. I wonder whether all those exercises with Rounding To The Nearest have any actual impact on habits of life.  Would it be more useful to explore “when would you round, and how much would you round?”

We should revisit it more often, too.   “Round to the nearest whatever” is one of those weird isolated skills that Show Up On Assessments and people dont’ remember how to do, even if they actually do know a thing or two about math.   (I need to coin a term for that…)  It’s like Knowing What The Associative Property is.   People apply it left, right and sideways — but get the “which property is this?” questions wrong.

Then there are the students who leave off all the other numbers and round 1,239 to … 40.

That’s where I talk about what rounding *is* — and that it’s for where we don’t care about the little pieces.   Money and miles are often good references.   How long is this trip?  Well, I’m not *exactly* sure… but 1239 is not close to 40, is it?

Then for my overwhelmed-by-the-symbols folks, who will think 1,247 rounds to 1300 because there’s a big ol’ 7 out there, yes, I’ll teach “underline the number in the place you’re supposed to round to, and circle the next smallest place because that’s the guy you care about (or, circles and arrows Arlo Guthrie style– hey, it’s almost Thanksgiving…):

round_4 (from https://www.tes.com/lessons/YaJiCXw8P1WRdQ/comparing-and-rounding-decimals )

We’ll talk about how the other places are tinier and tinier… 21,199  is closer to 21,000 than to 22,000.  Number lines help…

I like the roller coaster idea, too, where 5 is at the top (I especially like the one where the person in the bin is leaning forward at ‘5’ and I could say ‘ so really, it’s half way, and if you’re an accountant you try to find a way to go up half the time and down half the time, but our culture generally says “GO BIG!” so let’s do that here…)    but the pictures I’ve found are on Pinterest and that’s always a dead end as far as actually getting to the sources…  and since I’m the “help with the assignment” person, that hasn’t gotten to a priority for getting it on the wall the way the big number line and the pictures of perfect squares did.

Now to get back to that attempt to make a Canvas course and figuring out how to make Something Better for Adults who Need To Understand Math happen… grants, fellow connivers…

 

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