If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

## 4th grade foundations (Eureka Math/EngageNY)

### Course: 4th grade foundations (Eureka Math/EngageNY) >Unit 3

Lesson 1: Topic A: Foundations

# Comparing areas and perimeters of rectangles

Sal compares the areas and perimeters of rectangles to a given rectangle. Created by Sal Khan.

## Want to join the conversation?

• can you explain what the video was talking about it was not clear HELP? PLEASE
• sure i can try email back if you don't understand this is what he said:
to like find the area you need to times the way up & down to the way side to side to find the area!ok understand for the perimeter is like the out line or measure of an shape!

bye
• how can i find the area of a circle
• Interesting question for third grade! This is usually taught in seventh grade.

First we need two definitions.

The radius of a circle is the distance from the center to any point on the edge.

The number pi is a decimal with infinitely many digits that starts 3.14159265358979323... .
So pi is near 3.14. Pi is also near the mixed number 3 and 1/7.

Then the area of a circle is pi times radius times radius.

Have a blessed, wonderful day!
• how do you know the answer this guy is a genius
• Well, for the perimeter you have to add all the sides of the rectangle. In the video, the pink rectangle's perimeter would be 34 since the 4 side's lengths of the rectangle are 12, 12, 4, and 4. Adding those numbers; 12+12+5+5 = 34. The 12 and 4 may not be shown on the other side but it's the same length.

To get the area of a rectangle, you have to multiply the two sides which are not the same. For example, the blue rectangle has 2 sides whose lengths are 4 and 15. If you calculate 4 times 15 you get 60. Note, that to get the area of a rectangle you don't multiply all the sides, just the 2 different ones (4 & 15 in this example).

The area and perimeter formula can be used for any rectangle. Try doing the exercises, and use the formula listed above to get it.

Hope this helps.
• How can I find the area of a circle?
• Area of a circle: pi x radius squared
• This is a random question, but who found out about Area & Perimeter?:)
• Um, I think you can't really indentify one person. Ever since humans started building things, we started measuring them for precision.
• I need help on area can you help?
• Think of finding the area of a figure as counting the number of smallest (unit) squares that can fit inside the figure. For a rectangle, these unit squares can be counted by multiplying the number of units long by the number of units wide. In short: area of a rectangle is length times width.

Have a blessed, wonderful day!
• How do you find the area of a triangle