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Lesson 4: Multiply to find area

# Finding missing side when given area

Lindsay finds the missing side length on a rectangle when given the area of the rectangle.  Created by Lindsay Spears.

## Want to join the conversation?

• Can someone tell me what area means?
• Area is the space inside a shape.
• I was working on the area of the quadrilaterals but couldn't find the answer to this question. The question was "A square rug has an area of 72.25ft squared. What is the length of one side?" How do I solve it?
• Find the square root of 72.25.
• how do you find the width when you have no length?
• If the area is given then the formula would be: (area/width=length) because (length x width = area)
• How would u find area of a figure/shape if you didn’t have cut out squares?How would it be labeled?
• There would be lines stretching from side to side of both the width and the height . That’s how they would be labeled, and you would multiply the length of the width and the of the height to get your answer.
• why is area so hard
• Lindsay Spears is saying that our area is 80 square centimeters and it is not 80 square centimeters it's 10 square centimeters cm.
• can someone tell me what this is?
• just divide 24 by 4 to get 6 that easey
• Can someone tell me what areaLindsay finds the missing side length on a rectangle when given the area of the rectangle. Created by Lindsay Spears.
• The area that Lindsay finds is through some basic algebra and arithmetic knowledge. As she begins with the `Area = 80cm²` and a `Length = 8cm`.

Using the area formula `(L x W = A)`, we can input a few numbers, the same as Lindsay did!:

``8cm x ? = 80cm²``

However, there is an issue, we are missing a number! So, what we need to do is use our knowledge from the past lessons and use the commutative property and realize that the equation `8 x ? = 80` is also equal to `80 / 8 = ?`, so let us do that!

``80 / 8 = 10``

Now, with this answer, we can verify:

``10 x 8 = 80 √``

So, in conclusion, we have the following values:
Length (L) = 8cm
Width (W) = 10cm
Area (A) = 80cm²

That is how Lindsay did it!

Hope this helps!
(1 vote)
• the Answer just came to me
(1 vote)

## Video transcript

- [Voiceover] The picture has an area of 80 square centimeters. What is the width of the picture? So here's our picture, this super fun giraffe listening to music and our picture's shape is a rectangle and we're asked to find the width of that rectangle. Well, maybe we don't know a special formula or a special equation to find width, but we do know one to find area of a rectangle, so let's use that formula and see how it can help us. We know that area of a rectangle can be found by multiplying the length of the rectangle, over here, the length, times the width. So if we multiply the two side lengths of a rectangle, we get its area. And on this picture, in this rectangle, we are told that our area is 80 square centimeters, so we already know the area, and we can use that to help us. We also know the length. We're told that this distance from here to here, this length is 10 centimeters, so the length is 10. Times the width, we don't know the width. That's what we're looking for. So what we do know though, is that we need our width to be a number that when it's multiplied times 10, we get 80 for an answer. So what number times 10 equals 80 is eight. Eight time 10 equals 80. So that means the width of our picture is eight centimeters. Let's try one more. A rectangle has an area of 24 square meters. The width of the rectangle is four meters. What is the length of the rectangle? So this time we don't even have a picture to look at, but we have enough information up here to solve this. Again, we can use our formula that tells us area of a rectangle is the length times the width. Now we could draw this rectangle. It might be helpful to visualize it, but I'm gonna show you here, we can actually solve it without ever even seeing the rectangle, because we know the area is 24 square meters, so the space the rectangle covers is 24 square meters, and the length, we don't know the length. We're asked what is the length. But we do know that the width is four meters. So our length has to be some number that when it's multiplied times four, we get 24 for the answer. And that number must be six, because six times four equals 24. So the length of our rectangle is six, and in this case we're talking about meters, meters.