yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Finding missing side when given area | Math | 3rd grade | Khan Academy


2m read
·Nov 11, 2024

The picture has an area of 80 square cm. What is the width of the picture?

So here's our picture: this super fun giraffe listening to music. 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 the width, but we do know one to find the area of a rectangle. So let's use that formula and see how it can help us.

We know that the 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.

In this picture, and this rectangle, we are told that our area is 80 square cm. 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 cm.

So the length is 10 times the width. We don't know the width, that's what we're looking for. What we do know, though, is that we need our width to be a number that when it's multiplied by 10, we get 80 for an answer.

So what number times 10 equals 80? It's 8. 8 times 10 equals 80. So that means the width of our picture is 8 cm.

Let's try one more: a rectangle has an area of 24 square m. The width of the rectangle is 4 m. 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 the 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 going to show you here we could actually solve it without ever even seeing the rectangle because we know the area is 24 square m.

So the space the rectangle covers is 24 square m, and the length—we don't know the length; we're asked what is the length—but we do know that the width is 4 m.

So our length has to be some number that when it's multiplied times 4, we get 24 for the answer. That number must be 6, because 6 times 4 equals 24.

So the length of our rectangle is 6, and in this case, we're talking about meters.

More Articles

View All
Searching For Life in Volcanoes and Other Extreme Environments | Nat Geo Live
JEFFREY MARLOW: As a scientist, we often go to some of the most extreme places on our planet to collect microbes, bring ‘em back, understand what they’re doing and how they work. These types of organisms can actually broaden our search for life beyond ear…
American attitudes about government and politics | US government and civics | Khan Academy
What we’re going to do in this video is think about how the core beliefs of U.S. citizens impact their views on the role of government. What I’m going to do is talk about a few core beliefs that are often associated with the United States. But take it wit…
HOW TO INVEST $100 PER WEEK ASAP
What’s up you guys? It’s Graham here. So in the last few months, this channel has grown more than I ever would have imagined. Because we have so many new people joining us, I think it’s really important that we get back to the basics and discuss some of t…
China Is About To Cause A Global Recession
Two of the world’s biggest economies, the United States and China, are struggling. Business activity in Shanghai was brought to a standstill for weeks. Disastrous. I think there is no other word for it. What’s up guys? It’s Graham here. Throughout the la…
Unwanted Visitors- Deleted Scene | Life Below Zero
What I’m doing is the last people that were here, they’re supposed to bring some of their own tarps, spread them out, use their stuff. Um, but instead they use mine. Common courtesy would dictate cleaning them. That’s what I ask: hey, if you’re going to u…
Khan Academy Ed Talks featuring Asst. Supt. Beth Gonzalez - Thursday, Dec. 17
Hi everyone! Sal here from Khan Academy. Welcome to the Ed Talks live stream subset of the Homeroom. We have a very exciting conversation with Beth Gonzalez, Assistant Superintendent of Detroit Public Schools. So, start thinking of questions for Beth, and…