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## 4th grade

### Course: 4th grade > Unit 8

Lesson 5: Adding and subtracting mixed numbers- Adding mixed numbers with like denominators
- Subtracting mixed numbers with like denominators
- Add and subtract mixed numbers (no regrouping)
- Mixed number addition with regrouping
- Subtracting mixed numbers with regrouping
- Add and subtract mixed numbers (with regrouping)

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# Subtracting mixed numbers with regrouping

Sal practices subtracting mixed numbers with common (like) denominators. Items require regrouping (borrowing).

## Want to join the conversation?

- How was he able to do all that regrouping.(15 votes)
- regrouping here is a lot like the normal regrouping in subtracting whole numbers. You "borrow" from the next place value over so you can do the subtraction(12 votes)

- i need 10 votes plz

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:,;.;.;.;.;.;.;.;.""|<<\'|:/#(10 votes) - why doesn't khan academy have a video about subtracting mixed numbers from whole numbers? if it does, where is it?(7 votes)
- Subtracting mixed numbers from whole numbers is really basic. You first subtract the whole number parts and find the difference. You then reduce the difference by 1, keep that as the whole number part, "copy and paste" the denominator of the mixed number into the denominator of the difference, then subtract the value in the denominator of the mixed number by the value in the numerator (of the mixed number), then put that difference into the answer's numerator.

In other words, subtracting mixed numbers from whole numbers means you are subtracting mixed numbers by mixed numbers, except the fraction part of the mixed number of what is actually a "whole number" equals 0.(6 votes)

- how do you do that hard math(7 votes)
- it is easy you just turn the wholes into fractions then add and then you are going to be able to solve it vinelk6417(2 votes)

- But why did he change the 4 to a 3, is he subtracting?(4 votes)
- why did people create fractions they are annoying(1 vote)
- Well Lexi, fractions are just a portion of a whole. If we didn't have fractions, we'd have to pay at least a dollar for EVERYTHING. With fractions, we are able to purchase things for a quarter (1/4), a half dollar (1/2), or even forty cents (four dimes, also known as 4/10 or 40/100).

There are lots of good reasons for fractions. Keep practicing and sooner or later you'll find they are fun.(9 votes)

- Leave a smiley face if you like cats!^. .^(5 votes)
- give a upvote if you don't know me(4 votes)
- I will vote everyone.(4 votes)
- This is very hard but this video will teach me!(4 votes)

## Video transcript

- [Instructor] So let's
see how we could approach four and 1/4 minus two and 2/4. Pause this video and have a go at that before we work on this together. All right, so the first thing
that you might try to do is re-write this as four
and 1/4 minus two and 2/4. And the reason why it's
useful to write it this way is we could say look,
each of these mixed number have a whole number part and then they have a fractional part. And so I could try to
subtract the fractional part from the fractional part and then the whole number part
from the whole number part. And that will often work. But when we go to just
the fractional parts and we say hey, how do
I subtract 2/4 from 1/4, 2/4 is larger than 1/4. You immediately might find yourself in something of a conundrum. So what do you do? Well, what comes to the rescue
is a notion called regrouping and that's that we're not
just subtracting 2/4 from 1/4. We're subtracting two and
2/4 from four and 1/4. So what we could do is we
could take some of the value that's in this four and
regroup it into the fraction. What do I mean by that? Well instead of four, if I view four as three and 4/4, 4/4. And so 4/4 plus 1/4 is 5/4, 5/4. So I could re-write this as three and 5/4 minus two and 2/4. Once again, why is that useful? Because 5/4 is greater than 2/4. What is 5/4 minus 2/4? Well that's going to be 3/4. And then what is three minus two? Well that's going to be one. And we get one and 3/4. Another way we could of thought about it is this is the same
thing as four minus two plus 1/4, plus 1/4, minus 2/4, minus 2/4. And we have trouble
with the 1/4 minus 2/4. That's what we saw right over here. So what we do is we take some
of that value from the four. Instead of four we could
re-write that as three plus 4/4. That's the same thing as four. And of course you have minus
two plus 1/4 minus 2/4. And then if you add the 4/4 to the 1/4 that's going to give us 5/4. So you're going to have three minus two. That's that part and that part. And then you're going to have if you add the 4/4 and the 1/4, so plus 5/4 minus 2/4. And that exactly what we have here. Three and 5/4, three and 5/4 minus two, minus two, and minus 2/4. And so three minus two is one. 5/4 minus 2/4 is 3/4.