Lesson 7.1/7.2 Add/Sub Decimals

Adding and Subtracting Decimals

Objective: I can determine sums and differences by adding and subtracting decimals in order to fluently add and subtract multi-digit decimals using the standard algorithm.

Multiple Choice

Julie and Doug are building a tree house out of wood boards. Julie has a board that is 1.15 meters long and Doug has board that is 0.7 meter long. What is the combined length of their boards?

Two students solved the problem. Who is correct?

• Ryan's Work

• Claire's Work

Adding Decimals

Adding decimals is like adding whole numbers. Before you add, line up the decimal points. This will make sure you are adding the correct place values together.

Subtracting Decimals

Do the same thing when you subtract decimals. You may need to regroup.

Open Ended

What is an important rule to remember when adding or subtracting decimals?

Numbers without a decimal point

If a number does not have a decimal point, add the decimal point at the end of the number.

Multiple Choice

How do you write the number 824 as a decimal?

• 8.24

• 0.824

• 82.4

• 824.0

Ready to try it?

Watch the two examples your teacher presents, and then you will get to practice and test your skills.

Fill in the Blanks

What is the sum of 4.3 + 4.16?

Fill in the Blanks

What is the difference of 2.17-0.8?

Fill in the Blanks

What is the combined length of the Lost Horse Mine trail and the Mastodon Peak trail?

Lost Horse Mine Trail: 6.4 km

Lost Palms Oasis Trail: 11.6 km

Mastodon Peak Trail: 4.8 km

Skull Rock Trail: 2.7 km

Fill in the Blanks

How much longer is the Lost Palms Oasis trail than the Skull Rock trail?

Lost Horse Mine Trail: 6.4 km

Lost Palms Oasis Trail: 11.6 km

Mastodon Peak Trail: 4.8 km

Skull Rock Trail: 2.7 km

Multiple Choice

Exit Ticket #1

Lia and James went to the movies. The tickets are $3.00 each.  Lia bought popcorn and a slushy for $8.50 together. James bought a slushy and nachos $12.00 together. How much money did they spend total?

• 26.50
• 2.650
• 3.00
• 53.65

Multiple Choice

Exit Ticket #2

8.42 - 7.3

• 15.72

• 1.72

• 1.12

• 15.12