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Area with partial grids

Explore the concept of finding area with partial arrays. Learn how to determine the area of partial rectangles by completing the rectangle with lines, similar to a grid. Created by Sal Khan.

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Video transcript

- [Teacher] We're told, "The following rectangle is partially split into unit squares. What is the area of the rectangle above?" So pause this video and see if you can figure that out. Alright, now let's do this together. So first it's good to just know what do they mean when they say area? Well, they say it's partially split into unit squares. When they're talking about a unit square they're talking about a square like this. And when we're talking about area, we're talking about how many of these unit squares would exactly cover this entire shape. That many unit squares would be the area of this entire rectangle. So how could we do that? Well, what we could do is we could keep drawing these lines that have already been partially drawn, and we can then see how many of these unit squares we have. So let's just finish drawing these lines here. I'll try to draw it as neatly as I can. So we have that. We have that like there. And then let me complete this one, and let me complete that one. I'm almost done. That one and then that one. And so what we have here, let's see how many rows do we have? We have 1, 2, 3, 4, 5 rows. And in each of those rows, let me do it this way, five rows. And in each of those rows, how many squares do we have? Let's see, we have 1, 2, 3, 4. So you could view it as, we have five rows of four. So how many total of these unit squares exactly cover this rectangle? Well, we could just count them. We could see that that is going to be, well it's gonna be five rows of four. So it's gonna be one row, that's four. then another four, then another four, and then another four, and then another four. And let's see, yep, I have five fours here. I'm adding the five rows of four each there. And what is that going to be equal to? Well, this is going to be equal to four, plus four is eight, plus four is 12, plus four is 16, plus four is 20. So the area of the rectangle above is going to be 20. And it's important to say, "20 of what?" It's 20 square units. Or maybe I could say unit squares. Either way. But I'll call it square units. And we are done.