About this video
The video practises estimating multi-digit division by rounding to numbers that are easy to divide in your head. 794 / 18 becomes 800 / 20 = 40, and 722 / 68 becomes 700 / 70 = 10; then you pick the answer choice closest to the estimate.
You'll be able to
- round the numbers in a division problem to friendly numbers.
- divide the rounded numbers mentally, for example by dividing top and bottom by 10.
- choose the answer choice closest to my estimate.
Key words
- estimate
- A quick answer that is close to the exact one, usually found by rounding.
- approximately equal
- Close to but not exactly the same value.
- numerator and denominator
- In 800/20, 800 is the numerator (top) and 20 is the denominator (bottom).
Transcript
- [Instructor] What we wanna do in this video is get some practice estimating multi-digit division problems. Here, we're asked to estimate 794 divided by 18. Now, if you wanted to get the exact answer you'd probably have to do, in fact you would have to do, some long division or maybe use a calculator.
But, the whole point here is to get some practice estimating. Pause this video and try to see if you can figure this out without even using any pencil or paper. All right, so now let's do this together. I'll tell you what my brain does. My brain says that look, 794 is awfully close to 800 and then 18 is close to 20.
I would say this is going to be roughly the same thing as 800, is gonna be roughly equal to 800 divided by 20. Is it going to be exactly equal? No, but these are the numbers closest to the numbers there that it's easy for me to divide in my head. For example, I would then say, if I was just doing this purely in my head, I would say, well, 100 divided by 20 is five, so 800 divided by 20 is equal to 40.
Another way to think about it, 800 over 20. If we divide the numerator and the denominator by 10, it's the same thing as 80 over 2, which is equal to 40. So 794 divided by 18 definitely isn't exactly 40, but it's going to be close to 40, and especially of these choices right over here.
It's definitely gonna be much closer to 40 than 80, 4, or definitely 400. So, we're gonna go with that. Let's get another example here, make sure we get enough practice. Once again, we are asked to estimate 722 divided by 68. Why don't you have a go at it. Pause the video and try to see if you can figure out what it is and try to do it in your head.
Well, what I would do in my head, I would say, well look, 722, this is awfully close to 700, and 68 is awfully close to 70. And then, this is quite straightforward to do in your head, 700 divided by 70 is going to be equal to 10. And, good for us, there's a choice here that is awfully close to what we approximated.
Now, if you don't find your exact answer here, that's okay 'cause remember, it's an approximation. You should find the answer that is closest to what you estimated. But, whoever wrote this question had a very similar thought process. They said, okay, 722, pretty close to 700.
And 68, pretty close to 70. And so it's gonna be approximately equal to 700 divided by 70.
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