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## Arithmetic

### Course: Arithmetic>Unit 5

Lesson 3: Regroup whole numbers

# Regrouping whole numbers: 675

Sal regroups 675 into various addition problems. Created by Sal Khan.

## Want to join the conversation?

• I'm not understanding the concept of regrouping whole numbers in this video lecture. Are subtracting from these whole numbers to simplify the equation? I'm lost on this information. Crossing the numbers out and throwing lower numbers don't tell me anything. I throw my hands up in the air.
• So I think where people get confused on this is that they're trying to figure out WHY you would want to do this. Under normal circumstances, you probably wouldn't sit down and actually write all of this out. The idea here is that you can take a number and break it down into many different combinations of parts and still end up with the same total.

200 = 100 + 100
200 = 50 + 50 + 50 + 50
200 = 13 + 37 + 50 + 100

and so on...

You get the idea. It's just a basic concept.
• regrouing is important in math why?
• The concept is used as the basis for other things like borrowing and carrying.
• What if a zero is in the thousands place when you regroup your number?
• It would be 0 thousands. For example 11527 would be 1 ten thousands + 1 thousands + 5 hundreds + 2 tens + 7 ones and could be regrouped to be 1 ten thousands + 0 thousands + 15 hundreds + 2 tens + 7 ones
(1 vote)
• I am now lost. Why are we giving a hundred a way? If you add 100s to the tens, doesn’t that mean you turn the 100s into thousands? Like, what’s the point of all this regrouping thing?
• when i type my awser it says they understand but it is not right
(1 vote)
• is 45+45=50 67+4=71
(1 vote)
• its asking us to regroup 754,like the video
(1 vote)
• when its like 86 and they say round to the nearest hundred how do I do that
• Let's say you want to round 123 to the nearest hundred. You look at the number to the right of the one you want to round to.
You want to round to the nearest hundred, so the place just to the right of that is the tens place. If that number is 5 or bigger, you round up. If it's 4 or smaller, you round down.
So with 123, the number in the tens place is a 2. That's 4 or smaller so you round down. 123 becomes 100.
Now let's look at 289 rounded to the nearest hundred. The number in the tens place is an 8. That's 5 or bigger so we round up. 289 becomes 300.

But what happens with numbers like 89?
Same thing. You want to round to the hundreds place so you look at the number in the tens place. What is it? 8. That's 5 or bigger so we round up. That means we have to increase the number that's in the hundreds place by 1. So what number is in the 100's place? 0. What's the next number up? 1. 89, rounded to the nearest hundred, is 100.
• Can someone please clarify why I would ever want to regroup whole numbers? I do not think I have ever done so...