Estimating large differences
About this video
The video estimates two differences by rounding to the nearest thousand. 29,224 - 18,793 is about 29,000 - 19,000 = 10,000, and rounding to the nearest ten thousand gives the same answer. 76,371 - 2,842 is about 76,000 - 3,000 = 73,000.
You'll be able to
- estimate a difference of large numbers by rounding to the nearest thousand.
- explain that different ways of rounding can give similar estimates.
- subtract thousands in my head.
Key words
- estimate
- A close answer found using rounder, easier numbers.
- difference
- The answer to a subtraction.
- approximately equal to
- Roughly equal; shown with a squiggly equals sign.
- round
- Change a number to the nearest ten, hundred, thousand and so on.
Transcript
- [Instructor] All right, we're asked to estimate 29,224 minus 18,793. This squiggly looking equal sign, that means roughly equal to or approximately equal to. So pause this video, have a go at this before we do this together. All right, so the way I think about it, both of these are in the tens of thousands.
We could round to the nearest 10,000. If we wanna get a little bit more precise, we could round to the nearest thousand. So let's go with the nearest thousand, see what happens. So let's see, 29,224 is closer to 29,000 than it is to 30,000, so let's say this is approximately or roughly going to be equal to 29,000 minus, now, 18,793, that's closer to 19,000 than it is to 18,000, so let's say that that's roughly 19,000.
And this we can do in our head, 29 minus 19 is 10. This is 29,000 minus 19,000, so this would be 10,000 right over here, which is exactly one of these choices. Now, you might not get exactly this, but you should just get when you estimate, 'cause there's many different ways to estimate, whichever is closest.
For example, you could have rounded to the nearest 10,000. In that case, you would've said that this is roughly equal to 30,000 minus 20,000, which would've actually also have given you 10,000. So that's just a case where even if I do it two different ways, I still would've gotten that same answer.
Now let's do another example here. So here we're told to estimate 76,371 minus 2,842. Pause the video and have a go at that. All right, well, these, and 2,842, I'm not even in the tens of thousands, so maybe I just wanna definitely round here to the nearest thousand, so this is closer to 3,000 than it is to 2,000.
So let's say that this is, well, lemme do the 76,000 first. If I round to the nearest thousand, it's closer to 76,000 than 77,000, so this is roughly equal to 76,000 minus, and the second number is closer to 3,000 than 2,000, and so if I subtract, we can do that in our heads, that is going to be 73,000, which is exactly one of these choices here.
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