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## Arithmetic

### Course: Arithmetic > Unit 12

Lesson 3: Subtracting decimals intro# Estimating decimal subtraction

This video is all about learning to estimate when subtracting decimals. It emphasizes the importance of rounding to the nearest whole number and doing quick mental calculations to get an approximate answer. It's all about getting comfortable with estimation!

## Want to join the conversation?

- Upvote me please if you do thank you for sporting me(45 votes)
- nah im chillin fam(0 votes)

- but how do you know if you round up or down?(11 votes)
- You look on the digit on the right of the one you're rounding. If that digit is 5, 6, 7, 8 or 9 you round up. If it's 0, 1, 2, 3, 4 you round down.

That's all, hope that helps.(17 votes)

- i dont even know how to do vis(6 votes)
- let me help you! let me give you a example! so 12.93-6.1 forget the point and whats after it, and then turn it the closest number up so it is 13-6 = you know that right? after you get that bring back the point and whats after it and there you go!(13 votes)

- How does this work I am having a hard time understanding this(8 votes)
- what you can do is for instance 12.93-6.1 round both numbers to the nearest full number which would then be 13-6 and thats bascially it!(0 votes)

- this kind of dose not help.(4 votes)
- how does it not help Anl395005? what are you stuck on? may i help you?(5 votes)

- What’s the use of upvoting or downvoting I don’t get it

And why do people put useless comments saying upvote me

You’re not get anything useful from that

Other than a useless achievement(4 votes) - Why are there upvotes and downvotes? It's never really made sense to me.(3 votes)
- ijust put it on speed(2 votes)

## Video transcript

- [Instructor] Alright,
now let's get some practice estimating, subtracting decimals. So, over here it says 12.93 minus 6.1 is approximately equal to what? This squiggly-looking equal sign you can view as roughly equal
to or approximately equal to. So, pause this video and see
if you can figure it out. And, you shouldn't
really need paper for it. The whole point of estimation is to be able to do it quickly
and get close to the answer. You don't have to get the exact answer. Well, let's think about it. The way my brain would do it is 12.93-- Let's just round each of them to the nearest whole number. So, this is going to
be approximately 12.93 if I round to the nearest one or to the nearest whole number, I'm gonna round up to 13. And 6.1, if I round to
the nearest whole number, I'm gonna round down to six. So, I could say this
is roughly 13 minus six which is equal to seven, and that is indeed one
of the choices there. And, when you're doing estimation, you might have gotten a
slightly different result, but I'm guessing that the way that this question was set up, that if you do any type
of reasonable estimate, that you're going to have a number that is closer to seven than
any of the other choices. And to be clear, sometimes you
could do this in your head. For example, 12.93 minus 6.1, you could say 12 minus
six is going to be six. And then you have 93 hundredths minus, you could do this as 10 hundredths. So, it's gonna be 93
hundredths minus 10 hundredths is 83 hundredths, plus .83. So, just like that, you could do something like this and say, alright, the answer here
is gonna be 6.83 exactly. And that, once again, is
approximately equal to seven. But, the whole point of this exercise is to get comfortable estimating things because a lot of times in life you don't need the exact answer. You just need a rough answer, just to know the ball park
of what you're talking about. Let's do another example. So here, we are asked what is 56.75 minus 46.9 approximately equal to? Once again, pause this video
and try to work it out. Well, here I'm gonna do the same thing. I'm just gonna round each
to the nearest whole number and then subtract. And, I'm gonna write it out, but you could do this in your head. So 56.75 rounded to the
nearest whole number is 57 round up, minus 46.9, I would also round up to 47. And, in our head this is
pretty straightforward. This is going to be equal to ten. And, that is indeed is one of the choices. And, normally in life
when you're estimating, you don't have choices like this. I guess this is just the easiest way for-- This if off of the Khan Academy exercises. So, for someone to be able to grade it because estimations can be different, so you have to pick
the one that's at least closest to what you came
up as your estimate. Now, let's do one more example. And, I will write in purple. Alright. So, pause the video again. See if you can figure this out. Alright, so 49.7, I'm
gonna round up to 50, 4.16 I'm gonna round down to four. So, that's going to be
approximately equal to 30-- Oh sorry, that's gonna be
approximately equal to 46. And, we do indeed see
46 as one of the choices right over there. So, hopefully you feel comfortable. There's nothing fancy going on here. The whole point of this
is to just get comfortable doing things like this in
your head and estimating and rounding numbers so you
can get a ball park sense of what this difference is going to be.