# Adding and Subtracting Decimals - PowerPoint PPT Presentation

1 / 10

Adding and Subtracting Decimals. Lesson 1-5. The Basic Steps:. Line up the numbers by the decimal point. Fill in missing places with zeroes. Add or subtract. Addition Properties. Commutative Property of Addition: Numbers can be added in any order. Example: 5+3=3+5.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Lesson 1-5

### The Basic Steps:

• Line up the numbers by the decimal point.

• Fill in missing places with zeroes.

Example: 5+3=3+5

Associative Property of Addition: Numbers can be grouped in any way.

Example: (7+3) + 5 = 7 + (3+5)

Identity Property of Addition: The sum of any number and zero is that number.

Example: 18 + 0 = 18

### Mental Math

• Addition properties can be used to quickly find sums.

• Example: What is 52 + 12.4 + 48?

• First, change the order: 52 + 48 + 12.4 ________________ property.

• Then, group the first two addends together: (52 + 48) + 12.4________________ property

• 100 + 12.4 = 112.4

commutative

associative

### Why Estimate?

• Before adding your numbers, use one of the estimating strategies you learned to see what the answer should be close to.

### Example: 28.9 + 13.31

This can estimate to 30 + 13, which is 43. (Compatible numbers)

28.9

0

+

13.31

42.21

The answer is close to the estimate.

### Subtracting

• The addition properties do not work for subtraction.

• Estimate and subtract to find what the answer is close to.

• Subtract to find the real answer.

### Subtracting Across Zeroes

• If you have several zeroes in a row, and you need to borrow, go to the first digit that is not zero, and borrow.

• All middle zeroes become 9’s.

• The final zero becomes 10.

0

1

4 9 9 10

.000

15

-

9.372

5

.

6

2

8

### Classwork

Use this site to play MATHFROG- ADDING AND SUBTRACTING FRACTIONS

Homework Time!

P. 27, 1-49 odd