For more information, please see full course syllabus of Basic Math

For more information, please see full course syllabus of Basic Math

## Discussion

## Study Guides

## Practice Questions

## Download Lecture Slides

## Table of Contents

## Transcription

## Related Books

### Adding and Subtracting Decimals

#### Related Links

- Decimal
- Number
- Rational number
- 10
- Base
- Positional notation
- Decimal representation
- Addition
- Subtraction
- Approximation

- When adding and subtracting decimals, align the decimal points first
- Then, add or subtract the digits
- Place the decimal point in the same place

### Adding and Subtracting Decimals

6.23 + 7 + 0.825

462.9 − 84.27

145.3 + 23.2

915.2 + 20.3 + 0.26

0.05 + 0.55 + 0.25

120.25 − 50.55

- $ 100 − $ 50.50

- $ 120.80 − $ 45.65

450.89 − 20.85

165.32 − 10.385

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.

Answer

### Adding and Subtracting Decimals

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

- Intro 0:00
- When Adding and Subtracting 0:06
- Align the Decimal Point First
- Add or Subtract the Digits
- Place the Decimal Point in the Same Place
- Check by Estimating
- Examples 1:28
- Add: 3.45 + 7 + 0.835
- Find the Difference: 351.4 - 65.25
- Extra Example 1: Adding Decimals 5:32
- Extra Example 2: How Much Money? 6:09
- Extra Example 3: Subtracting Decimals 7:20
- Extra Example 4: Adding Decimals 9:32

### Basic Math Online Course

### Transcription: Adding and Subtracting Decimals

*Welcome back to Educator.com; this lesson is on adding and subtracting decimals.*0000

*When you add and subtract decimals, there are some rules to follow.*0008

*The first thing, the most important thing, is to align the decimal points.*0013

*Whenever you have decimal numbers and you have to add or subtract them, make sure the decimal point is lined up.*0018

*For example, if you are going to add 4.1 with 3.2,*0027

*you have to make sure that the decimal points, this and this, line up.*0036

*We are adding these numbers together; this becomes 3; this is 7.*0047

*After you add them, you have to make sure you place a decimal point in the same place.*0055

*You just align them straight down right here.*0059

*4.1 plus 3.2 is going to be 7.3; check by estimating.*0065

*4.1 is very close to 4; 4 is the whole number that it rounds to.*0073

*4 plus 3; this 3.2 rounds to 3; so it is about 7.*0077

*That is what it means to check by estimating.*0085

*Let's do a few problems; add 3.45 plus 7.835.*0088

*Again the first rule, the very important rule, is to line up the decimals.*0099

*Make sure you align them; 3.45.*0103

*The next number, we don't see a decimal point here.*0110

*7 doesn't have a decimal point; it actually does; we just can't see it.*0114

*If we have a whole number that doesn't show a decimal point, then the decimal point is right behind it.*0118

*It becomes 7.0; 7 is the same thing as 7.0.*0126

*If you have a whole number with no decimal point, that does not show a decimal point,*0132

*just place the decimal point at the end of it, right behind it.*0136

*I need to make sure that the decimal point goes right there; align them.*0141

*This one, 0.835; again 0.835, align the decimal.*0149

*That is all that matters; when you add them or subtract them, this is the main thing.*0159

*You don't line up the numbers; you line up the decimals.*0165

*We are adding these together.*0169

*Here, whenever I have decimals, I can place 0s at the end of them.*0170

*As long as it is behind the decimal and it is at the end, we can add as many 0s as we want.*0176

*Here it is behind the decimal point and it is at the end.*0182

*I can put 0s here to fill in those blanks.*0186

*If I add straight down, this becomes 5; 5 plus 3 is 8.*0191

*4 plus 8 is 12; 7 plus 3 plus 1 is 11.*0197

*My answer is 11.285 or 11 and 285.*0206

*The next problem, find the difference.*0215

*This is--write the first number--351 and 4 tenths, minus... be careful here.*0217

*If I write it like this, this would be wrong; this is wrong.*0229

*I have to make sure not to line up the numbers but line up the decimals.*0242

*65 and 25 hundredths; I have space right here; I have to put something there.*0251

*It is behind the decimal point and it is after the number so I can place a 0 there.*0266

*I can only place 0s if it is behind the decimal point and it is at the very end.*0272

*0 minus 5, remember I have to borrow; this becomes 3; this becomes a 10.*0277

*Get 5; 3 minus 2 is 1; decimal point comes down.*0284

*Again I have to borrow here; this becomes 4; this becomes 11.*0291

*11 minus 5 is 6; 4, again I have to borrow; this becomes a 2.*0298

*14; this becomes 8 and then 2; this is the answer.*0305

*Make sure your decimals are lined up.*0314

*Don't forget again if you have any empty spaces, you have to place 0s in them*0318

*because it is behind the decimal point and it is after the number so you can place 0s there.*0325

*Let's do a few more examples.*0331

*The next one, we want to add these two numbers, 123.1 and then 140.*0334

*We have a whole number that does not show a decimal point.*0343

*In that case, we are just going to place it at the very end.*0346

*It is going to be 140.0; adding these numbers.*0350

*It is 1; bring the decimal point down; 3; 6; and 2.*0358

*Next example, Sarah has 90 dollars and 75 cents.*0371

*Running shoes cost 55 dollars and 45 cents.*0377

*How much money will Sarah have left after buying the running shoes?*0381

*If she is going to buy something that costs 55 dollars and 45 cents, this is how much she has.*0386

*We have to see how much she will have left; we have to subtract the numbers.*0392

*She has 90 dollars and 75 cents; she spent 55 dollars and 45 cents.*0401

*I am going to subtract them; this will be 0; 3.*0412

*Again I have to borrow; this is 8; this is 10.*0421

*10 minus 5 is 5; this is 3.*0424

*After buying the running shoes, Sarah will have 35 dollars and 30 cents left.*0429

*The next example, we are going to subtract these two numbers.*0442

*Just write it out; 7 minus... be careful here.*0449

*The decimal place has to line up with this decimal place.*0455

*I am going to write 9 under the 2; 91 and 386 thousandths.*0458

*Again I have an empty space right here that I have to fill in with a 0.*0469

*Don't forget that; the reason why you have to place that 0 there.*0476

*If I don't have a 0... let's say I don't have a 0.*0480

*When you subtract this, this seems like it would be a 6 right here.*0486

*It seems like you would write a 6 here.*0491

*But if you place a 0 there, then you know that you have to borrow.*0494

*This is actually 10 minus 6.*0497

*If I borrow this, this is going to become 6; 10; 4.*0501

*Borrow again; 7; 16; there is 8.*0507

*7 minus 3 is 4; bring down the decimal point.*0514

*I am going to make this a 10; this becomes 11; this becomes 5.*0520

*10 minus 1 is 9; 11 minus 9 is 2.*0527

*5 minus 0 is 5; there is my answer.*0533

*If you want to check your answer by estimating, this is about 600.*0540

*If you just round it to the nearest hundreds, it is 600.*0546

*Here, this is about 90 or maybe let's say 100.*0550

*600 minus 100 is about 500; we have 500 something; it sounds right.*0554

*If we had let's say 50 something as our answer, we know that is wrong*0562

*because we know that if we estimate, it should be around 500.*0566

*The last example, adding these decimals together.*0573

*We have 8 and 215 dollars and 49 cents and 75 cents.*0578

*Remember the rule when we add or subtract decimals is to line up the decimal point.*0586

*That is very, very important.*0591

*When we have a whole number that is not showing a decimal point,*0593

*then we can place a decimal point at the end of it.*0597

*Just because it is not showing a decimal point does not mean it does not have one.*0601

*This is 8 point... and then I can add 0s to it.*0607

*8 dollars is the same thing as 8.00.*0610

*Then I am going to add 215 and 49 cents; line up the decimal point.*0614

*It is going to go 215.49; 75 cents here is going to be 0.75.*0621

*Going to add these all up together; 9 plus 5 is 14.*0637

*1 plus 4 is 5; 5 plus 7 is 12.*0646

*Bring down the decimal point; come straight down.*0655

*1 plus 8 is 9; plus 5 is 14; 1 plus 1, 2; and 2.*0660

*We are adding money together; don't forget your dollar sign.*0669

*This is your answer--8 dollars plus 215 dollars and 49 cents plus 75 cents becomes 224 dollars and 24 cents.*0674

*That is it for this lesson on adding and subtracting decimals.*0686

*Thank you for watching Educator.com.*0689

0 answers

Post by Tom Miller on January 16, 2017

In one of the practice questions is states that John has $120.80 and running shoes are $45.65. But then the question is how much money will Sarah have after she buys the running shoes.

1 answer

Last reply by: Dante Danis

Sun Dec 10, 2017 8:30 PM

Post by colton falgoust on May 19, 2014

K I'm stuck find the deference 120 .25 - 50.55. K u start with 5-5=0 next I borrowed 1 from the zero and made the two a 12 and made the zero a ten 5-12=7 10-0 how do u get 9 out of 10-0 any help so I can move to the next problem

0 answers

Post by yun wu on July 5, 2013

Good lesson

0 answers

Post by Fahad Chandia on June 20, 2013

good lesson

1 answer

Last reply by: Mashrur Elahi

Mon Apr 1, 2013 6:21 PM

Post by Ramez Hajelsawi on March 9, 2013

GOOD LESSON I LOVE IT :)

0 answers

Post by Nik Googooli on August 27, 2012

perfect,, really teacher,,, a real teacher,,,,, simple,,,,,