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Lesson 1: Area and perimeter

# Comparing areas word problem

Sal compares the area of two posters using their side-lengths. Created by Sal Khan.

## Want to join the conversation?

• Are there any other ways to calculate area?
• 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.
• Video transcript for you: 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 by 20 inches 20 inches so it might look something like that so the area 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 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 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 so we can immediately just throw it let's see 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 to 78 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 whose 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 - 720 would be 60
• why would you put that much.
• how to measure a shapes like croissant or star I mean is there a way to measure it in details ?
• 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.
• I still do not understand it! I am getting upset / mad!
• Are there any other ways to calculate area
• What if you were given the area but had to find the perimeter r?
• Do we have to use this way?