Rounding
Model Addition
How to use place value to round
numbers.
How to use models to add decimals.



there are different ways to round
numbers
rounding can be used to estimate sums
and differences
models and place value can be used to
add decimals to the tenths or
hundredths
Add decimals like 0.72 + 0.45 by shading
10-by-10 grids.
Use rounding to estimate differences like
8.72 – 3.05.
5.6
One way to estimate the difference is to
round each decimal to the nearest tenth.
8.72
– 3.05
rounds to →
rounds to →
8.7
– 3.1
5.6
0.72 + 0.45 = 1.17
Add Decimals
Properties of Addition
How to add decimals.
How to use properties of addition to add
decimals.


line up the decimal points and add the
digits in the same place-value position
bring the decimal point straight down in
the sum


Solve addition problems like 7.54 + 1.8.
1
7.54 Step 1 Line up decimal points
+ 1.80 Step 2 Annex a zero.
9.34 Step 3 Add digits in the same placevalue position
Step 4 Bring down the decimal point
the Commutative and Associative
Properties of Addition can be used to
add decimals mentally
it is helpful to group decimals together
that add to whole numbers
Add numbers like 1.5, 6.4, and 3.5
mentally by using properties of addition.
1.5 + 6.4 +
3.5
= 1.5 + 3.5 + 6.4 Commutative
Property
= (1.5 + 3.5) + 6.4 Associative
Property
= 5 + 6.4
Add.
= 11.4
Add.
Model Subtraction
Subtract Decimals
How to use models to subtract decimals.
How to subtract decimals.

models and place value can be used to
subtract decimals to the tenths or
hundredths
Solve subtraction problems like 0.65 - 0.28 by
shading 10-by-10 grids.

You can subtract decimals by lining up the
decimal points and subtracting the digits in
the same place value.

If you need to, you can annex, or add a
zero to the end of a decimal so that all the
decimals end in the same place value.
Subtract decimals like 15.42 – 3.6 and use
addition to check the answer.
There are 3 tenths and 7 hundredths left.
So, 0.65 – 0.28 = 0.37.
Check 15.42 – 3.6 = 15.42