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

Decomposing shapes to find area (subtract) | Math | 3rd grade | Khan Academy


2m read
·Nov 11, 2024

What is the area of the shaded figure? So down here we have this green shaded figure, and it looks like a rectangle, except it has this square cut out in the middle.

So when we find its area, we can think of it exactly like that. We want to know how much space it covers; it covers this rectangle's amount of area with this square cut out.

So what we can do is find the area of the larger rectangle and then cut out or subtract the area of the square to see what's left in this shaded area.

So let's start by finding the area of this larger rectangle, and to do that we can look at the side lengths. It has side lengths of 9 and 8. To find the area of a rectangle, we can multiply the side lengths. So 9 times 8 is 72.

That means that this rectangle covers 72 square centimeters. This entire rectangular area covers 72 square centimeters. But now we need to cut out or subtract the area of this square because that's not part of our shaded figure. We need to cut that part out.

So to do that, we know the side lengths are four on the square. So we can think of this as four centimeters across. So we can divide it into four equal sections, and same going this way.

And then, if we connect these lines, what it will show us is that we have—it's not drawn perfect—but we have four rows of four square centimeters. Four times, we see four square centimeters. This top row: one, two, three, four, and so on, four rows.

So there are 16 square centimeters we need to cut out of the 72 of this entire rectangular area. We need to cut out or subtract 16 of these square centimeters.

So let's do that. We have 72 as the entire area, and then let's start subtracting. I subtract out 10 of them just because, for me, I like subtracting 10s because they're simpler.

So 4, 8, 10 of the square centimeters. Now we're down to an area of 62 left. And then, let's subtract those two more; it will get us to—subtract two more will get us to sixty.

And then there's four left to subtract in order to subtract all 16. So 60 minus four gets us to 56.

So the entire area of 72, we subtracted out these 16 square centimeters, leaves us with a final area of 56 square centimeters.

More Articles

View All
How much of sales is conscious vs subconscious?
How much of sales is conscious and subconscious? I’m not really sure if there’s a measurement. Definitely conscious of what you want to say. If you’re not thinking of what you’re saying, then you get yourself in trouble. That’s usually what they call peop…
Looking for Killer Whales 26 Years After the Exxon Valdez Oil Spill (Part 1) | National Geographic
In 1989, the largest oil spill in US history destroyed a remote Alaskan wilderness. That was a long time ago. Most people say the sound is back to normal, except for this man. He’s been studying killer whales caught up in the spill. He believes they’re st…
Three Ways to Destroy the Universe
One day the universe will die. But why? And how? And will the universe be dead forever? And how do we know that? First of all, the universe is expanding. And not only that, the rate of its expansion is accelerating. The reason: dark energy. Dark energy i…
How I built a $500,000 Net Worth at 24 Years Old
So I recently learned a very valuable lesson: don’t make a claim here on YouTube unless you’re willing to back it up. I recently talked about how lessons I have learned from billionaire investor Charlie Munger helped me build a $500,000 net worth at 24 ye…
Concrete and abstract nouns | The parts of speech | Grammar | Khan Academy
Hello Garans. So today I’d like to talk to you about the idea of concrete and abstract nouns. Before we do that, I’d like to get into some origins—some word origins or etymology. Um, so let’s take each of these words in turn. I think by digging into wha…
Finding decreasing interval given the function | Calculus | Khan Academy
Let’s say we have the function ( f(x) = x^6 - 3x^5 ). My question to you is, using only what we know about derivatives, try to figure out over what interval or intervals this function is decreasing. Pause the video and try to figure that out. All right,…