Video: Finding the Area of an Unknown Shape by Counting the Unit Squares Making up the Shape

Ryan made this sign for his yard sale; find its area.

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Video Transcript

Ryan made this sign for his yard sale; find its area.

We know that finding area is counting the number of square units. So we can count all the squares on this grid to find the area. But there are a few things we can do to make this a little easier. For example, the triangle part, here, of this figure looks like it might fit on the left end, here. And if that is the case, then we can treat this shape like a rectangle. We would need to find the area of the rectangle that I’ve highlighted in blue. But how can we know for sure that the triangle part fits on the end. If we measure the triangle on the right, it has a base of three and a height of six. The cutout on the left has a base of six and a height of three. The triangle on the right and the cutout on the left are the same size. Then let’s count the squares found inside this rectangle. There are 20 columns and there are six rows. If we multiply six times 20, we get 120.

There are 120 square units in our figure.

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