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- [Voiceover] We're told to fill in the blanks to complete the equation that describes the diagram. So let's think about what's going on over here. If we start at zero, and we move one, two, three, four spaces to the right of zero, this arrow right over here represents positive four. We already see that right over here in the equation. Then from positive four, from the tip of this arrow, we then go one, two, three, four, five, six spaces to the left. So what we just did here is we just added a negative six to the positive four. Positive four plus negative six. Where does that put us? Well we see it puts us one, two spaces to the left of zero and each of these spaces in this diagram are one. So two spaces to the left of zero is going to be negative two. This is fun. Let's keep doing more examples. Write an addition equation or a subtraction equation, your choice, so they're giving us some choice, to describe the diagram. Alright, let's see what's going on here. We're starting at zero and we're going one, two, three, four to the left. So if we're going four to the left or so we can say negative four, -4. And then we're going to go another one, two, three, four, five, six, seven, eight, nine to the left. So we could write this as negative four minus nine is equal to. And when you go four to the left and then you go another nine to the left, you end up 13 to the left of zero which is negative 13. Equals negative 13. So this way I've written it as a subtraction equation I guess you could say. Negative four minus nine, is equal to negative 13. Now another way I could have done it, I could have said negative four plus negative nine is equal to negative thirteen as well. Either of those would have been legitimate. Now I've written it as an addition equation. Let's keep going. Fill in the blanks to complete the equation that describes the diagram. So we're starting at zero, we go three to the left of zero, that's negative three. Then we go another three to the left of that. So we're going to add another negative three. We're going to add another negative three and that puts us six to the left of zero. Well six to the left of zero is negative six. And we're done.