Example: Adding 2-digit numbers (no carrying)
About this video
Sal adds 46 + 43 by adding the ones (6 + 3 = 9) and then the tens (4 tens + 4 tens = 8 tens) to get 89. He expands the numbers as 40 + 6 and 40 + 3 to show that the 4s in the tens place really mean 40.
You'll be able to
- add two 2-digit numbers without carrying by adding ones, then tens.
- explain that a digit in the tens place stands for that many tens.
Key words
- ones place
- The rightmost digit of a number, showing how many ones.
- tens place
- The digit to the left of the ones, showing how many tens.
- expanded form
- Writing a number as the sum of its place values, like 46 = 40 + 6.
Transcript
So we need to figure out what 46 plus 43 is. Let me write it down again and I'll write it like this: 46 plus 43. What we do here is we just first look at the ones place. We literally have 6 ones plus 3 ones, or you could say 6 and 3, and 6 plus 3 is just 9. 6 plus 3 is 9, so we have 9 ones.
And then you go to the tens place, and there's two ways to think about it. You could view this as 4 plus 4 is equal to 8, but really, the reality of what we're doing since we're operating in the tens place, this is really 40 plus 40 is equal to 80. And we could do the same problem expanded out.
This is the same thing as 40 plus 6. We've seen this before, right? That's what 46 is. And then 43 is the same thing as 40 plus 3. We've expanded these out before. And so when you add them, when you add a 6 plus a 3, you get a 9. When you add a 40 plus a 40, you get an 80.
So you get 80 plus 9, which is 89. And the whole reason why I did this is I wanted to show you that when you're adding 4's in the tens place, you're really adding 40's. The fact that it's in the tens place represents-- or the fact that the 4 is in the tens place shows that it represents 40.
The fact that the 8's there shows that it represents 80.
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