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Current time:0:00Total duration:2:35

CCSS.Math:

- [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.