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## Multi-digit multiplication

Current time:0:00Total duration:1:51

# Multiplying 2-digit by 1-digit

CCSS Math: 4.NBT.B.5

## Video transcript

Let's try to
calculate 3 times 32. And I like to rewrite it, and
this is one way of doing it. I like to rewrite it where I
have a larger number on top. So in this case it's 32. And I write the smaller
number right below it. And since the smaller
number is only one digit, it's only a ones digit, I
put that below the ones place on the larger number. So I'll put the 3
right over here. And of course, we can't forget
our multiplication symbol. And this is essentially a
way of saying the same thing. You could read
this as 32 times 3. But 32 times 3 is the exact
same value as 3 times 32. It doesn't matter what
order you multiply in. Now let's try to compute it. And once again, this is
only one way of doing it. There's many ways of doing it. And I want you to think
about why this works. We'll start with
this 3 down here, and we're going to multiply it
times each of the digits in 32. So we'll start with 3 times 2. Well, 3 times 2 from our
multiplication tables, and you can figure it
out even if you didn't know your multiplication
tables, is 6. So 3 times 2, I'll write 6 right
over here in the ones place. Now we're going to figure
out what 3 times 3 is. Well, once again, we
know that 3 times 3 is 9. And since I'm multiplying times
the tens place right over here, I'm going to put it in the
tens place right like this. So we're done. We got 32 times 3 is 96. And I really encourage you to
think about why this worked. And I'll give you a
little bit of a hint here. I'll give you a little bit of
a hint about why this worked. Remember, 3 times 32 is the
same thing as 3 times 30 plus 3 times 2. And if you look at
it that way, that's essentially what
this process did. We did 3 times 2 is 6. 3 times 30 is 90. You add them together,
you get 90 plus 6 is 96.