WEBVTT

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Teacher: Today during math class, we are going to be adding two-digit
numbers. And what we’re going to do today is we’re going to compare

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multiple strategies that you can use to solve problems, and in doing
so you can compare the strategies for similarities and differences and

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really think about when you might use one strategy over the other.

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So we’re going to look at two strategies: breaking numbers apart, and
we’re also going to look at the vertical addition algorithm. And to

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start, I’m going to be over here with breaking numbers apart. Our
problem is 34+28. So to break the numbers apart, you want to break the

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numbers apart into the tens and the ones. So 34 breaks apart into 30
and 4. And then the number 28 breaks apart into the number 20 and 8.

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The next step is to think about how you can add the ones together and
how you can add the tens together. So I’m going to draw lines to help

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me connect the numbers. So 4+8=12. And then I need to add the tens
together. So I have 20, and I’m adding that to 30, and that gives me a

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sum of 50. So once we’re here, the last step is easy. All you do is add the
numbers together, and we know that 50+12=62. So 34+28=62 over here.

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Next, what I’m going to show you is the vertical addition algorithm.
So a different strategy, but we’re still adding the same numbers,

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34+28. And if you notice over here, I’ve stacked the numbers on top of
each other so that they’re in vertical columns. So to start, I’m going

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to start in the ones column. I’m going to add 4+8. 4+8=12. And when
I’m solving with the algorithm, I need to think, “Only one digit can

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go here under my ones column, and 12 is a two-digit number.” So I need
to regroup, and regrouping means I’m thinking about how many groups of

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tens I have and how many ones I have.

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So with the number 12, I know I have 2 ones, and I know I have one
group of 10, so I’m going to write a 1 above my tens column. And now

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that we’ve regrouped and finished the ones column, I can then move on
to add in the tens column. And here I have the numbers 3+2, but I

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can’t forget about that one extra group of 10 that I regrouped. So
3+2=5, and if we have one more that equals 6. So here we solved

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34+28=62, and if you notice 62 is the same as 62. So both of our
strategies gave us the same answer.

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Now, I want you to think what else is similar or the same about these
two strategies besides just the same answer. Yes, Emma?

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Emma: You added the ones first and then the tens.

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Teacher: Oh, that’s such great thinking, Emma! We did, for both of the
strategies, I targeted thinking about my ones column or the numbers in

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the ones first, and then I moved on to my tens. And that’s really
important when you’re thinking about addition is to always start in

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the ones. Now even though we started in the ones for both of them, I
think you noticed that we regrouped for the algorithm, but we did not

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regroup when we were breaking numbers apart. Raise your hand if you
can tell me why we had to regroup when using the algorithm.

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So now that we’ve looked at both strategies, and we’ve had our
discussion about similarities and differences, it’s really important

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to think about in math that, while there are multiple ways to solve a
problem, thinking about what is the best way to solve it in certain

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situations. So, again, if you’re doing math in your head you might
want to use a breaking apart numbers strategy, and if you have a

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pencil and a piece of paper you might want to use the algorithm if
that’s going to be more efficient for you.

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So now that I’ve shown you one example, you are going to do this
problem next, and when you’re done you are going to choose…well,

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you’re going to solve it using one of the strategies, and when you’re
done you’re going to work with a partner and you’re going to discuss

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the similarities and differences between how you solved this problem.

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I’ll be walking around to answer questions or to provide help as
needed.