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## 4th grade (2018 edition)

### Course: 4th grade (2018 edition) > Unit 2

Lesson 3: Multi-digit multiplication: standard algorithm- Multiplying 2-digit by 1-digit
- Multiplying 3-digit by 1-digit
- Multiply without regrouping
- Multiplying: 2-digit by 1-digit (regrouping)
- Multiplying 3-digit by 1-digit (regrouping)
- Multiplying 4-digit by 1-digit (regrouping)
- Multiply with regrouping
- Multiplying 2-digit numbers
- Multiply 2-digit numbers

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# Multiplying: 2-digit by 1-digit (regrouping)

Sal solves 6x37. Created by Sal Khan.

## Want to join the conversation?

- So at2:04, the ansewr is 222?(5 votes)
- show 390*8*7 390 8 times 7=(5 votes)
- The only thing I want to know is how to do a problem like this:

It has two large numbers and a smaller one that could equal to a very large number like those I am battling on CTC Math, is there any advice?(2 votes) - That is true Nicolas but what if you had let's say 3678 x 57? That would be a little harder than doing the typical way, this is building onto harder and harder equations, hope this helps! :)(2 votes)
- how do u multiply 9 digit #"s(2 votes)
- ok so say you have 9x7 right! you would subtract 1 from seven which is six and you count from six till you get to nine. so how much do you count to get from six to nine? you get 3........EX. 6,7,8,9. you put the 6 and the three together and you have 63 and this method is for all number not just this one! I REALLY HOPE THE HELPED YOU!(1 vote)

- How do you multiply 3 digit numbers(1 vote)
- Y is my videos not working(1 vote)
- How would this be useful in the real world(1 vote)
- If you have a rectangle 11 inches wide, and 3 inches tall, and need to figure out how much carpet you would need to buy to fill this rectangle, you are able to calculate...

11*3= 33 you would need to but 33 square inches of carpet.(1 vote)

- At0:25does that mean you can change it around for every operation?(1 vote)
- No. It only works for multiplication and addition because they are commutative. Communitive means that no matter where your numbers are, you get the same answer.

Helpful?(1 vote)

- how do you move a decimal to make the answer to a multiplication problem(1 vote)
- Count how many number after the decimal and you do the same thing for answer(1 vote)

## Video transcript

Let's try to compute 6 times 37. And I'll show you one
way of doing this. And then in future
videos, we can look at other ways of
doing this and think about why this is
actually working. So what I like to
do-- and this is often called the standard
method-- is take the larger of the two numbers. It doesn't matter if you're
doing 6 times 37 or 37 times 6. They equal each other. 6 times 37 is the same
thing as 37 times 6. So what I like to do is I take
the larger of the two numbers, and I write it on top. So I'll write 37. And then the smaller
of the two numbers, which is 6, I'll write
it on the bottom. And I'll align it by
the correct place. This only has one digit. It's in the ones
place, obviously. So I can write the
6 right over here. And I'll write the
multiplication symbol like that. And this is just another way
of expressing 37 times 6, which is the same thing as 6 times 37. Now, what we do is
we go with this, the first place in
this lower number. And there's only one place here. It's only the number
6 right over here. And we're going to multiply
that times each of the digits up here. So first, we will
start with 6 times 7. So we're going to first
multiply 6 times 7. Well, you remember from
your multiplication tables, 6 times 7 is equal to 42. Now, we don't just
write 42 here. At least, not in
the standard method we wouldn't write 42 here. We'd write the 2 in
42 in the ones place. So we'd write that
right over there. And then we'd carry the 4
in 42 up to the tens place. Now we need to think
about what 6 times 3 is. Well, once again,
we know 6 times 3. 6 times 3 is equal to 18. But we can't just
write an 18 down here. We still have this
4 to deal with. So 6 times 3 is 18, but
we've got to then add the 4. So 6 times 3 is
18, plus 4 is 22. So it's 6 times
3, and then we're adding that 4 right over there. And that's how we get
our answer-- so 222.