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## 4th grade

### Course: 4th grade > Unit 3

Lesson 5: 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.

## Want to join the conversation?

- 201x4... easy! 1.Just multiply 200x4 2. Then multiply 4x1 3. Last add the products 800+4=804

I hope this helps(13 votes)- piece of cake bro(6 votes)

- Has anyone ever heard of lattice multipliation?(13 votes)
- Hi

is it always just me or are the videos easy but the test are really hard.

please answer

see you next time!(8 votes) - Hi!

My question is pretty random, but can you ÷ using the same standered way we're using?

I know it works for addition, subtration and multiplacation!

Please answer!! :D

Thanks!(7 votes) - can i have ten votes(3 votes)
- Would the method of adding each number a certain amount of times work as accurately? (E.g, 3 x 123 = 123 + 123 + 123) Thanks in advance!(2 votes)
- The method would work if you were able to add perfectly, making no mistakes - but humans make mistakes all the time. Adding 123 three times is something many people can do without making errors, but one day you will need to multiply 123 by 17.25, and adding a number a lot of times is a lot more time consuming and likely to lead to errors. Computers are good at doing things perfectly, so old computers were often designed to add many times rather than multiply.(3 votes)

- what are points for?(3 votes)
- my mom taght me this when i was 4-5 no cap(3 votes)
- If I do 35*80 do I first do 35*8 than add a 0 to my answer?(2 votes)
- I figured out that, in terms of tenths and hundredths, 3.8 is as good as 3.80...(2 votes)

- i got little bit confuse so i watch 3 time then i told my mom to give me answer is that ok(1 vote)
- uhh no that's cheating.......(4 votes)

## 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.