The document provides guidance on operations with decimals, focusing on how to create the largest sum from given numbers and demonstrating rounding techniques. It outlines step-by-step procedures for adding and subtracting decimals, emphasizing the importance of aligning decimal points and using placeholders when necessary. Additionally, the document includes practice problems and collaborative activities to reinforce understanding of decimal addition.

1. Largest Number
• Using the following numbers: 5,3,7,4,2,1
create the largest sum possible. Each
number has one decimal in it.
• Example: 12.3 + 98.4 = 110.7
Decimals:

2. Place Value
• The decimal divides the whole numbers
from the parts. Think money. The decimal
divides the dollars from the cents.

3. Rounding
• To round any number, you use the place
value to the right to determine if the
number will increase or stay the same.
• Example:
• 1458.023508
• I want to round the thousandths place. I
need to look to the place to the right of the
thousandths place to determine what
happens to the number in the thousandths
place.

4. Guided Practice
• Round to the tenths place: 245.2653
• Round to the hundreds place: 12356.369
• Assessment Prompt: What two things do
we need to know to be able to round a
number?

5. Computing with Decimals
Adding and Subtracting
Decimals
Multiplying Decimals Dividing Decimals

6. Adding and Subtracting Decimals
Step 1: Line up the decimals in the addends
9.8
+ 2.12
Step 2: add or subtract as normal.
9.80
+ 2.12
11.92
Before or after you add or subtract you
need to bring the decimal straight down.
You may add a 0 to hold
the place value.

7. Adding and Subtracting Decimals
Step 3: If there are no decimals, then you are either
adding or subtracting a whole number. Remember the
decimal is behind the whole number.
6.93 + 3 =
Step 4: When subtracting, you may need to add zero
place holders to help you borrow.
3
- .123

8. Adding and Subtracting Decimals
Helpful Hints:
Think of decimal numbers as dollar amounts. This may
help you remember where to line up the decimals.
Rules for adding and subtracting are the same for
decimals as for whole numbers.
Whole numbers have decimals behind them. We
normally do not write them. Ex: 12 = 12.0
Don’t forget to put a decimal in your answer.

9. Adding and Subtracting Decimals
Your Turn:
2.3 12.06
+ 1.03 - 11.1
3.236 1.3
+ 1 - .265
7.5 + 6 = 4 - .67 =

10. Error Analysis
1 3 . 2 1 5
- 6 .2
1 3 . 1 5 3
11
1

11. Domino Addition
• Each student will have one domino. You
will match with another student to create
and solve a decimal addition problem. You
will do this 3 times.
• Put the partners’ names beside each
problem.

12. Summarizer
• What is the procedures for adding and
subtracting decimals?