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

Estimating adding large numbers by rounding


3m read
·Nov 11, 2024

Let's say that we run an egg farm. Yesterday, we went out and we collected 398 eggs from the chickens, and then today we went out and we collected 251 eggs from the chickens. What we're curious about is roughly how many eggs do we now have that we've collected over the last two days.

Well, there's a few ways we could do that. We could just add 398 to 251 and figure out what that is equal to. But let's say that we don't have a lot of time, and we don't have paper, and we want to do it in our heads. We don't care about the exact number; we want to know roughly how many eggs do we have.

Well, that's where the tool of estimating is useful. Instead of saying the exact amount of eggs, we could say how many do we roughly have, and that's what this squiggly equal sign means. It means, hey, we don't have to get the exact number, but how many do we roughly have? So we will be estimating.

The way that we can do that is we can round each of these numbers to a number that is close to them but that's easier to add in our heads, and then we add those two numbers. So pause this video and see if you can do that on your own before we do it together.

All right, now let's do this together. Let's start with 398 and let's round it to the nearest 10. 398, you can view this as we have a 9 in the tens place, but you could view this as 39 tens and eight. The 10 that it is right directly above is exactly 39 tens and zero ones, or 390. The next 10 would be, if we go up to 40 tens, which would be the same thing as 400.

Now, which one would we round to? Well, 398 is closer to 400 than it is to 390. We've talked about in the rounding videos that you can see that this right over here is 5 or greater, so we would round the tens place up. So we would round to 400. Thus, 398 we round to 400.

Next, we're going to add that to 251. What's that rounded to the nearest 10? So I'll do that again right over here: 251. The 10 that is right below that is going to be 250, and the 10 that is right above that is going to be 260. Again, you could view this as 25 tens and 1.

251 is clearly closer to 250. We can round down. Another way to think about it is, you look at the tens place and then you look at the ones place and you say, hey, this is less than five, so I'm going to round down on the tens place. We get to 250.

So when you round 251 to the nearest 10, you're going to get 250. Now I encourage you to add these two in your head. What would this be equal to? Well, the way that I think about it in my head, there are a lot of different ways to approach addition.

But you could say, all right, I have, I can think about the hundreds. I have four hundreds and I'm adding that to 200. Let me do this in a new color. So if I have four hundreds and I'm adding it to two hundreds, well, that's going to be six hundreds.

If I have zero tens and if I'm adding it to five tens, well, I'm still going to have five tens. And then, I have zero ones in either case, so I'm still going to have zero ones. And so there you have it. We were able to estimate 398 plus 251 as being roughly 650.

More Articles

View All
Analyzing model in vertex form
An object is launched from a platform. Its height in meters, x seconds after the launch, is modeled by h of x is equal to negative 5 times x minus 4 squared plus 180. So normally, when they talk about seconds or time, they usually would use the variable …
The Fascinating Lives of Bleeding Heart Monkeys (Part 3) | Nat Geo Live
Geladas aren’t afraid of all predators. You’re looking at the Ethiopian wolf. This occurs on the Guassa, and it’s the rarest canid in the world. There’s only about 400 remaining in Ethiopia, and 40 of them are at Guassa. They’re social, but during the day…
Worked example: calculating ion charge | High school chemistry | Khan Academy
So we’re asked what is the charge of a calcium ion with 18 electrons. So pause this video and see if you can work that on your own. I will give you a little bit of a tip: a periodic table of elements might be useful to see where calcium sits on that perio…
Watch Famous Ponies Swim in Chincoteague Island Tradition | National Geographic
[Music] There’s nothing else that I found that makes me as excited as I am to do this. You can’t ride roller coasters that give you this feeling. You can’t go other places and see anything like this. This is unique to here. We start on a Saturday. We wil…
Housing Expert: “Why Home Prices Will Crash In 2026”
What’s up you guys, it’s Graham here, and we got to talk about what’s happening with housing prices. Because despite record high values, constant increases, and the worst affordability in 40 years, there’s actually some good news in that a few major housi…
Marques Brownlee on Building an Audience and Other Advice for Creators
All right Marques Brownlee, how’s it going? Good, how are you? Doing well! So I’m curious, I’ve followed your channel for a while, but I definitely did not follow it in the beginning when you were reviewing software on your laptop. You’ve been doing it …