Adding and Subtracting
Decimals
Combine and Separate
Line Up Place Values
Add and Subtract and Compare

Suppose you go to a store and purchase a $21 item and a $8 item.

What would you say if the clerk added the items this way?

Would you pay $101?

Of course not!
21
+8__
101
When we round to estimate we can see the sum should be around 30 not 101.
20
+10
30
Place Value

The problem shows the numbers were not lined up correctly.

We need the place values to be lined up.

The 8 should be in the one's place

This answer is reasonable because
it is close to our estimated answer 30.

When adding, ones should be added to ones, tens to tens, and
hundreds to hundreds.

The same is true for tenths, hundredths, and thousandths.
21
+ 8
29
Understanding Place Value
Place Value Grid Models
Whole number grid models
Decimal Grid Models
Money
Decimal Grid Models
Recognize the Decimal
Decimal Problem Solver

Use blank tenths and hundredths grids to model the
decimal numbers in each problem.

Cut out and glue each problem and the decimal grids
onto construction paper to show how you solved it.
#1
Laura ran 0.4 miles one day and 0.3 miles
the second day. How many miles did Laura
run altogether?
+
=
#2 Juan biked 1.2
miles one day
and 1.5 miles
the second
day. How
many miles
did Juan bike
altogether?
.
+
___________________
.
Try on your own.
Add On your Marker Board

Follow the example: 2.3 + 4 + 5.027

Even whole numbers have a decimal.
2.3
4
+ 5.027

The 4 has a decimal after it.
2.3 + 4. + 5.027

Line up the decimal

Fill in zeroes

Add the place values

Round to the front number or the greatest place to estimate
2 + 4 + 5= 11
2.300
4.000
+ 5.027
11.327
Subtract on your Marker Board

Put the greater amount as the minuend
12.3
- 5.04

It might help to think of the numbers as dollar amounts
$12.30
- $ 5.04

Line up the Decimals

Fill in Zeroes

Be sure to regroup carefully

Estimate by rounding to the greatest place to ensure your answer is
reasonable.

Watch your teacher work through the problem on the board.

Does the teacher’s estimated answer show a reasonable answer?
On your Marker Board
To insure that like place values are added and
subtracted, we can line up the decimals.
*Work these. *Check with your partner.
*Discuss how you estimated by rounding to
the greatest place and are confident
your answer is correct.
#1 82.74
+ 6.05
#4 67 + 3.98
#2
145.12
- 23.00
#3 $ 38.54 - $12.76
#5 100 - 34.89
Watch the teacher work each problem. How did the answers
compare to the estimated answers? How did you estimate?
Are your answers close? Did you line the decimals?
Paper Assignment
Write the problem. Solve carefully. Then show the reasonable estimation.
#1 $16.34 + $5.78
#2 $120 – $46.37
#3
765.32 + 12 + 90.8
#4
87 – 64.95
#5
187.543 + 6.246 + 10.8 + 443.67
Be sure to round to the greatest place and estimate to see
if your answer is reasonable.
Grade/Check:
Use a red pen to self check your answers,
watch your teacher complete these after you have
completed yours on your paper.
Newspaper Assignment

Use the newspaper adds to find items to purchase.
Choose items that go together.
Example: bread, peanut butter, jelly. These items create a
sandwich.

Write the items and the prices,

Add the items.

Now decide the next greatest dollar to pay the cashier.
Subtract from the dollar amount you paid the cashier to
find your change.
Let’s start together!
Name
____________Newspaper Decimals____________________________
_________________________________________________________
2 items____________3 items __________4 items ______________
cake mix $ 1.09____________________________________________
icing + $ 1.29____________________________________________
_total _$ 2.38____________________________________________
_________________________________________________________
Pay with $ 5.00 __________________________________________
_______-_$ 2.38 ___________________________________________
change
$ 2.62___________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Review

Locate the decimals

Use the decimals to line up the place values

Use zeroes to organize

Be careful when regrouping

Check your answer

Does your answer make sense?

Practice

Yea! You got it!!