In this lesson, we will learn:

• How to add decimal numbers using base ten (block) models
• That adding decimal numbers is the same as adding whole numbers, which involves lining up the right place values and regrouping

Notes:

• To add decimals with base ten (block) models:
• Remember the three types of blocks used to represent the ones, tenths, and hundredths place values
• "One whole" or hundred block = ones place value
• Column (stick or rod) = tenths place value
• Single square = hundredths place value
• Count all of the blocks that you are adding up, altogether
• Regroup to get to your final answer. 10 of any type of block will regroup into the next bigger type of block.

• To add decimals, line up the decimal point to make sure you are adding the right place values in the same columns. Regroup (carry over) numbers whenever necessary.
• Sometimes, you will have to write one or more zeroes to a number after the decimal point (trailing zeroes) when the addends don't have the same number of place values.

#### Lessons

• Introduction
a)
How to add decimals with base ten (block) models

• 1.
Regrouping practice for decimals with block models
Regroup so that each place value only has one digit. Use base ten (block) models to help.
a)
17 tenths = ____ ones + ____ tenths

b)
4 ones + 12 tenths + 39 hundredths = ____ ones + ____ tenths + ____ hundredths

c)
6 ones + 29 tenths + 16 hundredths = ____ ones + ____ tenths + ____ hundredths

• 2.
a)

b)

c)

• 3.
Add the decimals by lining up on the grid. Regroup where necessary.
a)
34.8 + 5

b)
4.6 + 2.9

c)
41.03 + 5.72

d)
35.84 + 6.5

• 4.
Adding decimals and rounding decimal sums
a)
7.6 + 2.14

b)
80.65 + 19.23

c)
18.24 + 3.17

d)
98 + 38.97