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Course: Grade 5 (TX TEKS) > Unit 1
Lesson 1: Estimate addition and subtraction of whole numbers- Estimating multi-digit sums
- Estimate to add multi-digit numbers
- Estimating to subtract multi-digit numbers
- Estimate to subtract multi-digit numbers
- Estimating multi-digit addition and subtraction word problems
- Multi-digit addition and subtraction estimation word problems
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Estimating to subtract multi-digit numbers
Practice using estimation as a strategy to subtract multi-digit numbers to find the difference. Created by Sal Khan.
Video transcript
- [Presenter] So we have two
subtraction problems here that I want you to estimate. I first want you to estimate
what 51,384 minus 28,251 is, and then I want you to estimate what 761,423 minus 18,965 is. And this little squiggly equal
sign means approximately. So you're only creating an estimate. You don't have to do all
of the detailed math here. Pause this video and see if
you can figure those out. Alright, now let's work
through it together. I always enjoy estimating because it frankly requires less work. You're able to do things very roughly. So here, I have two
numbers that go all the way to the 10 thousandths place. So I'm just gonna round them
both to the nearest 10,000. So 51,384 rounded to the nearest 10,000 is 50,000 and 28,251 rounded to the
nearest 10,000 is roughly 30,000. So in my head, I would say
50,000 minus 30,000, well, that's going to be 20,000. So this whole thing is
approximately equal to 20,000. Now let's look at this
scenario right over here. This number goes up to
the 10 thousands place. Well, this number goes to
the hundreds thousands. So to make it consistent,
I'm going to round both to the 10 thousandths place. 'Cause if I just rounded this one to the a hundred thousands,
it'll just become zero and I wouldn't be subtracting anything. So if I round them both to
the 10 thousandths place, then this one is going to
be roughly equal to 760,000. And then this number is going
to be roughly equal to 20,000. If I round to the nearest 10,000 and on my head, if I said, okay, 760,000 minus 20,000, I
could do that in my head, that's going to be 740,000. So the difference of these two numbers is approximately 740,000, and I'm done.