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## Arithmetic (all content)

### Unit 3: Lesson 7

Multi-digit multiplication- Multiplying 2-digit by 1-digit
- Multiplying 3-digit by 1-digit
- Multiply without regrouping
- Multiplying 3-digit by 1-digit (regrouping)
- Multiplying 4-digit by 1-digit (regrouping)
- Multiply with regrouping
- Multiplying 2-digit numbers
- Multiplying 2-digit by 2-digit: 36x23
- Multiplying 2-digit by 2-digit: 23x44
- Multiply 2-digit numbers
- Multiplying multi-digit numbers
- Multi-digit multiplication

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# Multiplying 2-digit by 2-digit: 23x44

Learn to multiply two-digit numbers. In this video, we will multiply 23 times 44. Created by Sal Khan.

## Want to join the conversation?

- if i am multiplying by one digit numbers how do i divide to check my answer?(31 votes)
- you can also do that 9 x 9 =81 or if you want 81 = 9/81 = 9(4 votes)

- if im multipling by one digit how can i divide to check my answer(5 votes)
- Well, I suppose you would divide by one of the digits you multiplied by? 5*4=20. Check:20/4=5. Something like that.(4 votes)

- compute? very safisticated word what does it mean?(3 votes)
- In this context, the word "compute" means determining/finding the result by mathematical means. Or to put it a different way, you work out a problem's solution using calculation.(4 votes)

- Can I Divide To Check My Answer?(2 votes)
- Yes, you can because division and multiplication are like addition and subtraction; you can use one to check your answer.(1 vote)

- Doesn't of also mean to multiply(2 votes)
- How would solve this problem 55 time 11 cause I'm coming up with 650(2 votes)
- 55 times 11 is actually 605. When multiplying by 11, always multiply by 10 first and then add the number to your answer. i.e. 55 X 11 = (55 X 10) + (55 X 1)(1 vote)

- why can i not understand ?(2 votes)
- So, if you get a problem with 3 numbers you would just have more zeros, right?(2 votes)
- Assuming you mean three digits in the bottom row then yes you'd add two zeros when you got to the third digit because at this point you know your answer will be a multiple of 100.(1 vote)

- why do they put (23)(44)?(2 votes)
- Sal answers your question in the first part of the video, at0:10, when he says, "This could have also been written as 23 times 44, or they could have written it as 23 in parentheses times 44, so you just put the two parentheses next to each other. That also implies multiplication."

They put (23) next to (44) without the multiplication symbol in between them because the brackets/parentheses actually mean multiplication already.

If you put a number inside a bracket, what you are saying is also equal to that number times 1.

(23) is the same as 1(23) or 1 x 23

(44) is the same as 1(44) or 1 x 44

If you put another number outside the bracket without an operation symbol like division or addition, whether that number is in its own bracket or not, then what you are saying is to multiply the number inside the bracket by the number outside the bracket.

23(44) is the same as (23)(44) or 23 x 44

This is covered in more detail when you start learning Algebra.(1 vote)

- I'm not asking a question but sharing advice, the multiply sign has about 3 different symbols,a dot,the * sign,and the native X sign. Just for all yal who don't know.(2 votes)
- Yes, but it would be better to use the actual "dot sign" instead of just saying ( • ). On an Apple computer, press the following - option(alt) + 8. Hope this helps!(1 vote)

## Video transcript

Compute 23 times 44. And maybe the hardest part of
this problem, or maybe the first hard part, is to recognize
that that dot even means multiplication. This could have also been
written as 23 times 44, or they could have written it as 23
in parentheses times 44, so you just put the
two parentheses next to each other. That also implies
multiplication. So now that we know we're
multiplying, let's actually do the problem. So we're going to multiply 23--
I'll write it bigger. We're going to multiply
23 by 44. I'll write the traditional
multiplication sign there, just so that we know
we're multiplying. When you write it vertically
like this, you very seldom put a dot there. So let's do some
multiplication. Let's start off multiplying
this 4 in the ones place times 23. So you have 3 times 4 is 12. We can write 2 in the ones
place, but then we want to carry the 1, or we want
to regroup that 1 in the tens place. So it's 12, so you put
the 1 over here. And now you have 4 times
2 is 8 plus 1 is 9. So you can think about
it as 4, this 4 right here, times 23 is 92. That's what we just
solved for. Now, we want to figure out
what this 4 times 23 is. Now what we do here is, when you
just do it mechanically, when you just learn the process,
you stick a 0 here. But the whole reason why you're
putting a 0 here is because you're now dealing with
a 4 in the tens place. If you had another-- I don't
know, a 3 or a 4 or whatever digit, and you're dealing with
the hundreds place, you'd put more zeroes here, because we're
going to find out 4 times 23 is 92. We just figured that out. If we just multiplied this
4 times 23 again, we would get 92 again. But this 4 is actually a 40, so
it actually should be 920, and that's why we're
putting that 0. Now you're going to see
it in a second. So we have-- so let me put this
in a different color. So this 4 now we're
multiplying. 4 times 3 is 12. Let's put the 2 right here. It should be in the tens place
because this is really a 40 times the 3. Just think about it,
or you could just think of the process. It's the next space
that's free. 4 times 3 is 12. Carry the 1. This blue 1 is from last time. You ignore it now. You don't want to make
that mess it up. That's when we multiplied
this 4. So now we have 4 times
2 is 8 plus 1 is 9. So what we figured out so far is
4 times 23 is 92, and this green 4 times 23 is 920, and
that's because this green 4 actually represents 40. It's in the tens place. So when you multiply 44 times
23, it's going to be 4 times 23, which is 92, plus 40
times 23, which is 920. I just want to make
sure we understand what we're doing here. And so we can take
their sum now. Let's add them up. 2 plus 0 is 2. 9 plus 2 is 11. Carry the 1. 1 plus 9 is 10. Put a comma here, just
so it's easy to read, every third digit. So 23 times 44 is 1,012.