About this video
Mary's poster is 36 inches by 20 inches and Susan's is 26 inches by 30 inches. The video finds each area by multiplying (720 and 780 square inches), using tricks like multiplying by 2 or 3 and adding a zero, then subtracts to show Susan's poster is larger by 60 square inches.
You'll be able to
- find the area of a rectangle by multiplying its length and width.
- multiply by a multiple of ten, like 20 or 30, by multiplying by 2 or 3 and then by 10.
- compare two areas and find the difference by subtracting.
Key words
- area
- The amount of flat space inside a shape, measured in square units.
- square inches
- The unit for area when the sides are measured in inches.
- rectangular
- Shaped like a rectangle: four sides and four square corners.
Transcript
Mary's rectangular poster is 36 inches by 20 inches. Susan's rectangular poster is 26 inches by 30 inches. Which poster has a larger area and by how many square inches? So let's think about these. So this is Mary's poster. Mary's poster is 36 inches by 20 inches.
So it's 36 inches by 20 inches. So it might look something like that. So the area is going to be 36 times 20 square inches. 36 times 2 is 72. So 36 times 20 is going to be 720 square inches. Now let's think about Susan's situation. So let's draw Susan's poster.
Susan's poster is 26 inches by 30 inches, so 26 inches by 30 inches. So Susan's poster might look something like that. That's Susan's poster, my best attempt to draw a rectangle. What's the area here? The area is 26 times 30 square inches, which is equal to-- let's actually multiply this one out-- 26 times 30.
We could do 26 times 3 and essentially add a 0 there. So 3 times 6 is 18. 3 times 2 is 6, plus 1 is 78. And actually, I could have probably done that in my head. 3 times 20 is 60, plus 3 times 6 is 18, gets us 78. But this isn't 3 times 26. 3 times 26 would be 78.
30 times 26 is 780. So it's 780 square inches. So whose poster, which poster has a larger area? Susan's. Susan's poster has a larger area. And by how many square inches? Well, hers is 780 square inches while Mary's is 720 square inches. So it's by 60 square inches.
780 minus 720 would be 60.
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