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## 7th grade foundations (Eureka Math/EngageNY)

### Course: 7th grade foundations (Eureka Math/EngageNY)>Unit 2

Lesson 3: Topic C: Foundations

# Adding decimals: 9.087+15.31

Adding decimals is an essential math skill. To add decimals, such as 9.087 and 15.31, align the decimal points and place values. Fill in any missing digits with zeros to make the numbers the same length. Then, perform the addition as usual, starting with the smallest place value. The result of adding 9.087 and 15.31 is 24.397. Created by Sal Khan.

## Want to join the conversation?

• how did you get the decimals to line up with each other and why do you put a number off to the side
(217 votes)
• You line up the decimal points.

Wrong
``  1.23 +45.6------- 0.579``

Correct
``  1.23+45.60-------- 46.83``
(540 votes)
• how does this help us in a real life situation
(25 votes)
• You have to use decimals when go shopping. because if something cost 28.34 and then you also get another thing that costs 15.24 you have to add them so u know how much u spending
(30 votes)
• how do you do it
(15 votes)
• Use the decimals to guide the place value alignment.

• line up the decimals above and below,
then add each column of numbers,
• empty spaces are equal to zero

9.087 + 15.31 = ?
``   9.087+ 15.31—————————  24.397 ←🥳 answer``

★In Addition order doesn't matter, because it's Commutative, meaning we can rearrange addition and get the same answer,
1 + 7 = 8
7 + 1 = 8
So either decimal value can be first or second, but always line up the place values.
``  15.31+  9.087—————————  24.397 ←🥳 same answer``

★This method works for more than two values as well, as long as we always line up the decimals so that the place values form columns!

2.14 + 0.3421 + 3 + 11.2 = ?
``   2.14   0.3421   3+ 11.2——————————  16.6821 ←🥳 answer``

Rearranged,
with place keeper zeros…
``  11.2000   3.0000   0.3421+  2.1400——————————  16.6821 ←🥳 same answer``

★ Just remember: we must line up the decimals and keep the place values aligned throughout the calculation, move the decimal straight down, so it is aligned in the answer too, then it's just adding the columns like usual…

Start adding in the far right column, carry values to the left, etc…

(ㆁωㆁ) Hope this helps someone!
(24 votes)
• hi can i have a upvote
(12 votes)
• yes u can :>
(6 votes)
• his voice is nice :]
(13 votes)
• Yes it is very
(3 votes)
• I made a chart and placed them into the chart to solve it, is that smart?
(8 votes)
• yes, it is very smart! i learned how to solve it using a chart, and it's good that you still use it as a strategy! ^^
(11 votes)
• is it allowed to add an zero at the whole number?
(8 votes)
• I mean I get ur question. You can add a zero at a whole number. HOWEVER it won't change the answer. For example, 5+0=5. But it is allowed but no use.
(8 votes)
• The tip of adding decimals are that you should line up the decimal points together.
(10 votes)
• Sal is a good teacher
(9 votes)
• Is it compulsory to line the decimals
(5 votes)
• Corresponding place values must be added together, the decimals naturally align when the columns are in the correct order.

Therefore aligning the decimals is an easy way to align the place values correctly into columns for manual addition.

So, when creating accurate addition columns, it is also compulsory to line up the decimals.
(1 vote)

## Video transcript

Let's see if we can add 9.087 to 15.31. And I encourage you to pause the video and try to do it on your own. So I'm assuming you have tried to do it on your own. And now let's see how we could actually tackle this. Now, one thing I want to point out, some of you all might have seen these numbers all lined up and immediately want to say, hey, 7 plus 1 is 8, and 8 plus 3 is 11, carry the 1, et cetera, et cetera. And if you did that, you would be making a mistake. Because, you see, right over here, these decimals aren't lined up. Here, if you did that, you would be adding the 7 thousandths to 1 hundredths. You would be adding 0 tenths to 5 ones. You would be adding 9 to 1 tens, or essentially, this is a 10 right over here. So the places would be all mixed up. So what you need to do is to actually align the decimals so that your place values are aligned. So what you want to do is you want to align things up. So we could write 9.087. And then we want to align the decimal. So let's align the decimal. This is what has to match up. And this is going to be 15.31. And this should hopefully make sense to you as well. This is 9 point something plus 15 point something so it's going to be-- If you add 9 to 15, it will be 24 point something, give or take a little bit. And you see that here. Here you have a 9 plus the 15. So you have lined up the appropriate place values. And now we are ready to add. It's a good idea to start with the smallest place value, so if you have any extra at a certain place, you can bring something into the next place value. So here you say 7 plus-- well, this is 7 thousandths. It's in the thousandths place. And you might want to-- you say, well, what do I add it to? There are no thousandths right over here. And you're right. There are no thousandths. So we could literally write 0 thousandths. So 7 thousandths plus 0 thousandths is 7 thousandths. 8 hundredths plus 1 hundredth is 9 hundredths. 0 plus 0 tenths plus 3 tenths is 3 tenths. We got our decimal. Then you have 9 ones plus 5 ones is 14 ones. Well, 14 ones is the same thing as 4 ones and 1 ten. So we'll carry that 1 right over there. This is just 1 ten plus 4 ones, which is 14. And so then finally, you have 1 ten plus another ten is 2. So we get 24.397.