Video: Finding a Missing Number in a Given Addition Equation

Fill in the blank: _ + 3 = 7.

02:00

Video Transcript

Fill in the blank. What plus three equals seven.

In this addition equation, we’ve got a missing number. Now, often with an addition equation, the missing number comes after the equal sign. We need to add together two numbers to find out what that total or the whole amount is. But what’s different about the addition equation that we have here? The missing number is one of the numbers that we’re adding together. We know what they make because we can see that the addition equals seven. The whole amount is seven. Our addition equation also shows us one of the parts that makes up seven. And that’s the number three. Something add three equals seven. And what is that something? What part goes together with three to make seven?

We could count on to help us find the answer. And to do that, we could use a number track, so let’s do that. We could start by pointing to the number three. Let’s see how many numbers we need to count on to get to a total of seven, one, two, three, four. Three and four are two parts that go together to make a total of seven. So we could complete our part–whole model to show the number four. And we could also fill in the blank in our addition equation. We can make seven out of three and four. Four plus three equals seven. The missing number is four.

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