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## Algebra basics

### Course: Algebra basics > Unit 1

Lesson 8: Operations with decimals- Adding decimals: 9.087+15.31
- Adding decimals: 0.822+5.65
- Adding decimals: thousandths
- Subtracting decimals: 9.57-8.09
- Subtracting decimals: 39.1 - 0.794
- Subtracting decimals: thousandths
- Multiplying decimals example
- Multiplying challenging decimals
- Decimal multiplication place value
- Dividing decimals with hundredths
- Dividing by a multi-digit decimal
- Dividing decimals: hundredths

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# Multiplying decimals example

To multiply decimals, we multiply them just like whole numbers. We count the number of digits behind the decimal in both numbers we're multiplying, and make sure our answer has the same number of digits after the decimal. - We can check our answer by thinking about what it means to multiply by 0.5 (or one half). Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- Can you use Lattice multiplication while multiplying decimals?(260 votes)
- Yes. Draw your lattice, making sure to put the decimal in the correct place for each number. To figure out where the decimal belongs in your answer, put your fingers on each decimal in the numbers you multiplied together. Then, trace the decimals until your fingers meet at a corner in the lattice. Follow the diagonal from that spot to your answer. That is where your decimal belongs in the answer.(65 votes)

- how are some ways to multiply decimals(4 votes)
**Multiplying decimals is basically like multiplying non decimal numbers***Like so:*

`3.4`

`x`

`5.4`

`follow the same steps as:`

`34`

x`54`

=`1,836`

----------

00136

+ 170

-----------

`18.36`

*Always remember to line up your numbers correctly!*

*If you need more detail in this answer, or you want another method, feel free to let me know!*

*I hope this helps!*(30 votes)

- I think this is my life now -_-(13 votes)
- hi! are all decimals tenths?(7 votes)
- no. just like regular place value, you can have tenths, hundredths, thousands, and others like you do in actual place value.(17 votes)

- hi everyone this video was amazing to me. you guys should see if there is one on world history.(9 votes)
- At2:13why does zero have no value? Why is it allowed to be cut out?(6 votes)
- The zero is a placeholder. You can take it out if you want. Her is an example:
**placeholder --> 0.70 x 0.7**

They are both the same(0.7 and .7

hoped that helps!

Oh, and Yes, if there is nothing after a zero in the whole number (ex: 387.900), then, yes, it is allowed!(4 votes)

- can a world history teacher assign khan academy or just a core math teacher and an elective math teacher because I'm in middle school the sixth grade(5 votes)
- Can you switch the numbers around and multiply and get the same answer?(2 votes)
- This is called the commutative property of addition and multiplication. Only with addition or multiplication can you switch the numbers around. So 2x3=3x2. You CAN'T do this with division or subtraction. 6/3 = 2 whereas 3/6 = 1/2 or 0.5.(4 votes)

- sorry if this isn't about the topic, but what's lattice multiplication?

thanks,(3 votes)- it's a Hindu-style multiplication https://en.wikipedia.org/wiki/Lattice_multiplication(2 votes)

- They did it not correct because they didn't put the dot together. and I want to be big.(3 votes)

## Video transcript

We're asked to multiply 32.12,
or 32 and 12 hundredths, times 0.5, or just 5 tenths. Now when you multiply decimals,
you multiply them the exact same way you would
multiply whole numbers, and then you count the number of
spaces behind the decimal you have in your two numbers you're
multiplying, and you're going to have that many spaces
in your product. Let me show you what
I'm talking about. So let's just multiply
these two characters. So we have 32.12 times 0.5. And when you write them out, you
can just push both of them all the way to the right. You could almost ignore
the decimal. Right now, you should write the
decimal where they belong, but you can almost pretend that
this is 3,212 times 5, and then we'll worry about
the decimals in a second. So let's get started. So if we were just multiplying
5 times 3,212, we would say, well, 5 times 2 is 10. Regroup the 1. 5 times 1 is 5, plus 1 is 6. 5 times 2 is 10. Regroup the 1. And then finally, you have 5
times 3 is 15, plus 1 is 16. And then we don't have
any other places. If we were just doing this as
05, we wouldn't multiply 0 times this whole thing. We would just get 0 anyway. So just 5 times 3,212 gives
us this number. But now we want to care
about the decimals. We just have to count the total
number of spaces or places we have behind the
decimal point in the two numbers we're multiplying. So we have one, two, three
spaces, or three numbers, to the right of the decimals in
the two numbers that we're multiplying. So we need that many numbers to
the right of the decimal in our answer. So we go one, two, three, put
the decimal right over there. So 32.12 times 0.5 is 16.060. And this trailing zero right
here we can ignore, because it's really not adding any
information there. So we could just write
this as 16.06. The last thing you want to do
is just make sure that this makes sense. You have a number that's
almost 32, and we're multiplying it by 0.5. Remember, 0.5 is the same thing
as 5 over 10, which is the same thing as 1/2. So we're really multiplying
32.12 times 1/2. We're trying to figure out what
one half of 32.12 is. And half of 32 is 16, and half
of 0.12 0.06, so this makes complete sense.