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What Is 100 + 100?

1/6/2016

4 Comments

 

When is this true? 100+100 =/= 200 Explain your choice. #mtbos #mathchat

— John Stevens (@Jstevens009) December 18, 2015
Lately, I've been trying to wrap my head around different ways of getting students to understand the use of appropriate units. My current test subjects are 5 and 3, so it's tough to ask them questions that require the depth of response I'm looking for. Thankfully, there are plenty of willing folks on the interwebs of Twitter.

@Jstevens009 when you get two perfect scores on two tests.

— Megan Schmidt (@Veganmathbeagle) December 18, 2015
Ooooooh, I didn't think of that one! Nice job, Megan. In this case,
​100+100=100

@Jstevens009 When the units of the two groups are different. #unitchat

— Bree Pickford-Murray (@btwnthenumbers) December 18, 2015
Alright, Bree, way to rain on that whole parade. You didn't burst my bubble, but you did expose my plan...

@Jstevens009 100 tenths plus 100 ones does not equal 200. Too obvious?

— Alexandra Otto (@AlexandraOtto) December 18, 2015
That's one of the best parts about this, Alexandra - nothing is too obvious. When we start to realize that units matter, fun begins.

@Jstevens009 when you're buying 25-cent items from Amazon; two 100-item orders don't qualify for free shipping

— Tim (@timteachesmath) December 18, 2015
Tim, I must say that this one had me thinking. Especially since 95% of my Christmas shopping was done through the Big A, I was into it. 

So what?

None of this means anything if we don't address the issue: kids are notorious for leaving units out of their solutions. Nah, HUMANS are notorious for leaving units out of our solutions. In Chemistry, it would be virtually impossible to run through stoichiometry problems without following the units. When building a space shuttle, one mistake in units could, well, cost you a $125 million shuttle.

UNITS MATTER.

As I've continued to compile Would You Rather...? math posts, it has become clear that many of the decisions we make have a lot to do with the units in which they are presented. If we can get kids to play games with units more often, my conjecture is that we would have contributing members of society who are less susceptible to manipulation of the media and marketing. We would have contributing members of society who are more adept to the information presented to them. We would have contributing members of society who, ideally, look to a value's units before rushing to a judgement. Ideally.

I like the 100+100 because it seems "easy" for kids, but use whatever you think would be the most interesting for your group. Once a week, put up a different solution. The trick, the game, the goal, is to find out what units are being used to reach the solution.
​
Here are a few others:

When does 100+100=50?

— John Stevens (@Jstevens009) December 18, 2015

When does 100+100= 3 1/3?

— John Stevens (@Jstevens009) December 18, 2015

When does 100+100=60.96?

— John Stevens (@Jstevens009) December 18, 2015

When is 100+100=1.5625?

— John Stevens (@Jstevens009) December 18, 2015
What did you come up with? What did your students come up with? For ideas, think of all common units of measure (time, distance, money, etc.). Start simple, then get more complex as the students gain confidence.

Oh, and good luck with "I'magonna Google that".

 Happy Unit Fishing
4 Comments
Bree link
1/6/2016 03:36:42 pm

I like the final prompts, though it's not 100% clear to me how you lead up to them with a class. I don't think I'd be comfortable starting with those questions cold. Do you imagine starting with the very first tweet you sent out and then transitioning to the specific equations?

Reply
John link
1/6/2016 05:10:37 pm

Thanks for dropping by, Bree. When I taught middle school, I had a place on my board for riddles, puzzles, and math problems. For example, when is 8 + 5 = 1? It wasn't something that students were forced to do, but it was that challenging brain break for kids who needed it, and they seemed to enjoy it. I had them in mind for this. And yes, I would lead this type of questioning off with getting students to think about when 100 + 100 is not equal to 200. Here's what I would do:

Start class off with the challenge and see if they can work in pairs/groups to come up with something. If not, we leave it alone and continue with the day. Eventually, that student who tends to get off task migrates back to that problem and it gives his/her brain something else to focus on.

To be honest, once you've done one or two, it becomes a hunt to find the right units that make the problem true. For the first couple times doing this, would you introduce it and work through it with them? Maybe it wouldn't be a cold open, but could you see students asking good questions to get there? I'm not sure about those.

Reply
Judy link
2/4/2016 06:01:05 am

Am curious if using Notice and Wonder would help with the opening? Just thinking about Bree's question of how to push this idea out to kids.

Reply
Tracie
6/28/2017 07:49:19 pm

I can't wait to use this with fifth graders. Thanks for sharing your knowledge. This is a fabulous way for some students to find mindfulness.

Reply

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