Basic geometry and measurement
Sal compares the area of two posters using their side-lengths. Created by Sal Khan.
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- Are there any other ways to calculate area?(26 votes)
- Yes to find the area of a rectangle, multiply its height by its width. For a square you only need to find the length of one of the sides (as each side is the same length) and then multiply this by itself to find the area.(7 votes)
- how to measure a shapes like croissant or star I mean is there a way to measure it in details ?(11 votes)
- With more complex shapes, you're best served by dividing them into more simple forms and simple adding the areas together. A five sided star can be divided into 10 equal, obtuse triangles.(12 votes)
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.