Main content

### Course: 6th grade > Unit 2

Lesson 2: Subtracting decimals# Subtracting decimals: 9.005 - 3.6

Subtracting decimals is simple when you line up the decimal points and fill in missing zeros. Regroup when needed by borrowing from the whole number and adding to the tenths place. Mastering this skill helps with everyday calculations and improves overall math understanding. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- Who invented decimals and fractions???(204 votes)
- The earliest recorded use of place value (writing numbers in a line to represent larger numbers) is from the ancient Babylonians around 1800 BC. However, they didn't have a decimal point, or a concept for zero yet. They just had to write the numbers out and determine how large it was based on context.

Bonus fact: The Babylonians used a base 60 numeral system, which is where we get our measurements of time from (60 seconds to a minute, 60 minutes to an hour)(202 votes)

- Why do you have to line up the decimals when you add or subtract?(59 votes)
- If you don't line them up, you may add ones to tenths, tenths to hundredths, etc. and get wrong answers. Lining them up helps you add or subtract all the proper places and get a correct answer.(24 votes)

- How do you borrow from nothing?.(13 votes)
- go to the next place up, but if you cant go up, you made a mistake and ordered your question wrong or you have to subtract it negatively(13 votes)

- can someone explain this broadly because i do not get it(14 votes)
- why does this exist(8 votes)
- when your working with fractions if you get a number like 4.8 + 6.78 the .8 is basically 80 so it would be

4.80

6. 78(6 votes)- yes you can do that if it makes it easier(2 votes)

- why does this exist(4 votes)
- this is so easy u just carry the 4(3 votes)

- How can you do it when one number don't have a decimal?(3 votes)
- Put a decimal point just after the last (units) digit of the number, then write in the missing 0’s to the right of the decimal point.

Example: for the problem 37 - 15.48, you can write it as 37.00 - 15.48.

Have a good day!(2 votes)

## Video transcript

We need to calculate 9.005 minus
3.6, or we could view it as 9 and 5 thousandths
minus 3 and 6 tenths. Whenever you do a subtracting
decimals problem, the most important thing, and this is
true when you're adding decimals as well, is you have
to line up the decimals. So this is 9.005 minus 3.6. So we've lined up the decimals,
and now we're ready to subtract. Now we can subtract. So we start up here. We have 5 minus nothing. You can imagine this 3.6, or
this 3 and 6 tenths, we could add two zeroes right here, and
it would be the same thing as 3 and 600 thousandths, which is
the same thing as 6 tenths. And when you look at it that
way, you'd say, OK, 5 minus 0 is nothing, and you just
write a 5 right there. Or you could have said, if
there's nothing there, it would have been 5 minus
nothing is 5. Then you have 0 minus
0, which is just 0. And then you have a 0 minus 6. And you can't subtract
6 from 0. So we need to get something into
this space right here, and what we essentially are
going to do is regroup. We're going to take one 1 from
the 9, so let's do that. So let's take one 1 from the
9, so it becomes an 8. And we need to do something
with that one 1. We're going to put it
in the tenths place. Now remember, one whole
is equal to 10 tenths. This is the tenths place. So then this will become 10. Sometimes it's taught that
you're borrowing the 1, but you're really taking it, and
you're actually taking 10 from the place to your left. So one whole is 10 tenths, we're
in the tenths place. So you have 10 minus 6. Let me switch colors. 10 minus 6 is 4. You have your decimal right
there, and then you have 8 minus 3 is 5. So 9.005 minus 3.6 is 5.405.