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## Numbers & Operations - The Real & Complex Number Systems 201-210

### Unit 3: Lesson 4

Multiply with partial products# Multiplying 3-digit by 1-digit

CCSS.Math:

Learn to multiply a 3-digit number by a 1-digit number without regrouping. In this video, we will multiply 4x201. Created by Sal Khan.

## Video transcript

Let's multiply 4 times 2,012. Actually, let's make it
a little bit simpler. Let's multiply 4 times
201 just to simplify things a little bit. So 4 times 201. So as we've seen
in previous videos, I like to write the
larger number on top. This is just one of
many ways of tackling a calculation like this. I'll write the 201. And then I'll write
the 4 right below it, and I'll write it right
below the ones place. And so I have 201 times 4. Now, just like we did when
we were multiplying a one digit times a two digit, we do
essentially the same process. We first multiply 4 times the 1. Well, 4 times 1 we
know is equal to 4. So we put a 4 right over
there in the ones place. Then we can multiply
our 4 times the digit that we have in the tens place. In this case, we have
a 0 in the tens place. So 4 times 0, well,
that's just 0. 4 times 0 is 0. We put the 0 in the tens
place right over here. And then last, we have 4
times this 2 right over here. And so 4 times 2 is equal to 8. And we put the 8
right over here. And we get our answer-- 804. Now, why did this work? Well, remember,
when we multiplied 4 times 1, that was
literally just 4. And we've got that
4 right over here. When we multiply 4
times 0, that's 0 tens. So we've got 0 tens
right over here. And when we multiplied 4 times
2, this was actually a 200. It's in the hundreds place. So 4 times 200 is 800. So what we're essentially
doing by writing it in the right place is
we're saying, 4 times 201, that's the same thing
as 4 times 200, which is 800, plus 4
times 0 tens, which is 0 tens, plus 4
times 1, which is 4. So 800 plus 0 plus 4 is 804.