Transcript Adding and Subtracting Decimals

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:
Place Value
• The decimal divides the whole numbers
from the parts. Think money. The decimal
divides the dollars from the cents.
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.
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?
Computing with Decimals
Adding and Subtracting
Decimals
Multiplying Decimals
Dividing Decimals
Adding and Subtracting Decimals
Step 1: Line up the decimals in the addends
9.8
+ 2.12
You may add a 0 to hold
the place value.
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.
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
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.
Adding and Subtracting Decimals
Your Turn:
2.3
+ 1.03
12.06
- 11.1
3.236
+
1
1.3
- .265
7.5 + 6 =
4 - .67 =
Error Analysis
1 11
13.215
6 .2
13.153
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.
Summarizer
• What is the procedures for adding and
subtracting decimals?