### 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.