Video: Compare two addition expressions

Are they equal? 12 + 3, 9 + 6

01:50

Video Transcript

Are they equal? 12 plus three and nine plus six.

We need to add these numbers together in order to simplify. That way we can decide if they’re equal or not. So we can either use a calculator, count, or stack them together and add.

Let’s say we would count: 12 plus three. We begin with 12 and then we need to count three more numbers. 13 will be our first number, 14 will be our second number, and 15 will be our third and final number. So 12 plus three would be equal to 15.

We also could add them by stacking them together: adding the ones place together and adding the tens place together. So the ones place want us to add a two and a three. And two plus three is five. In the tens place, there’s a one and then technically a zero. So one plus zero is one. So once again, we get 15.

So now, let’s simplify nine plus six. So we begin with nine and then we count six more numbers. 10 will be our first, 11 will be the second, 12 will be the third, 13 will be the fourth, 14 will be the fifth, and 15 will be the sixth. So our answer will be 15. We can also stack them and add them. And in the ones place, there’s nine plus six which is 15.

If there had been numbers in the tens place, which we could represent here by zeros, we would want to carry that one up there to the tens place because the five goes into the ones and the one needs to go up to the tens place. So one plus zero plus zero is one. So once again, we got an answer of 15.

So are these equal? Yes, they are because they’re both equal to 15. So our answer is yes.

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