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### Course: Class 4 > Unit 2

Lesson 3: Multiply by 1-digit numbers# Multiplying 3-digit by 1-digit

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(18 votes) - Hi

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

please answer

see you next time!(14 votes)- agreed definatly(2 votes)

- Has anyone ever heard of lattice multipliation?(11 votes)
- I don't know what is "lattice multiplication".(2 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!(10 votes)- yes you can :D(3 votes)

- great job!but i still cant figure 1*1?(3 votes)
- Any number multiplied by 1 is the number itself. So 1*1 = 1, 1*2 = 2, 1*3 = 3, and so on. If you are a visual learner then think of it like this: if you have one group of strawberries and that group has one strawberry in it then how many strawberries are there? The answer is 1.(3 votes)

- He never finished the problem. His problem was 4x2012 which is 8048, but he did 4x201!(4 votes)
- Do we Always have to put the bigger number on top(4 votes)
- At1:50you said that 800 + 0 + 4 is 804. That is correct, but what is the reason to say 800 + 0 + 4 if the 0 doesn't have any value?(3 votes)
- He's trying to reinforce the concept that the numbers have different values based on their place, and how we keep track while we multiply. If it was 231 instead, it would work out to 800 + 30 + 4.(3 votes)

- how do you multiply 5s -10s ?(3 votes)
- First, I recommend using proper notation. to show multiplication, usually we write it as (5s)(-10s), where each factor is in parenthesis. if you prefer, an alternative is to write 5s * -10s with an asterisk. Next, to multiply what you wrote, start with the numbers: 5 * -10 = -50 since a positive times a negative yields a negative product. Second, multiplying variables, the exponents are added (according to rules of exponents). Therefore, s * s = s^2

For help with multiplying variables: https://www.khanacademy.org/math/algebra-basics/core-algebra-exponent-expressions/core-algebra-exponent-properties/v/exponent-properties-1

For help with multiplying integers (negative numbers and positive numbers): https://www.khanacademy.org/math/arithmetic/absolute-value/mult_div_negatives/v/multiplying-positive-and-negative-numbers(2 votes)

- if there is a zero, do i add a zero or minus one(3 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.