Session 22: Decimal- addition & subtraction

Introduction Activity (15 minutes):

Decimal Price Tag Game

Purpose: Activate prior knowledge and build context.

Setup:

Bring 5–6 small classroom items (e.g., pencil, eraser, notebook).

Label each with a price tag (e.g., $0.75, $1.20, $2.50, etc.).

Instructions:

Give each student or group a “shopping budget” (e.g., $5.00).

Ask them to “buy” 2–3 items and calculate the total cost and change from $5.00.

Discuss answers and write sample calculations on the board.

Transition:

"To shop smart, you need to be able to add and subtract decimal prices correctly. Today, we’ll learn how to do that like pros!”

2. Concept Teaching (15 minutes)

A. Place Value Review:

Draw a place value chart on the board (Ones, Tenths, Hundredths, Thousandths).

Ask students to place digits in the correct columns for 3.75, 0.08, etc.

B. Key Concept:

Always line up decimal points when adding/subtracting.

Add placeholders (zeros) if needed for consistency.

Demonstration:

   4.2  

+ 1.35  

------ 

  5.55

Explain the importance of matching decimal places.

Repeat with subtraction:

   5.00  

- 2.45  

------  

  2.55

Guided practice:  (40 minutes) 

Addition 

1.3.25 + 4.75

Answer: 8.00

2. 5.6 + 2.85

Answer: 8.45

3. 7.4 + 3.19

Answer: 10.59

4. 0.78 + 6.22

Answer: 7.00

5. 9.03 + 1.97

Answer: 11.00

6. 2.45 + 8.55

Answer: 11.00

7. 4.68 + 5.32

Answer: 10.00

8. 6.125 + 3.875

Answer: 10.00

9. 10.5 + 7.25

Answer: 17.75

10. 12.01 + 3.99

Answer: 16.00

Substraction 

1. 6.75 – 3.25

Answer: 3.50

2. 9.8 – 4.56

Answer: 5.24

3. 7.6 – 2.39

Answer: 5.21

4. 8.25 – 5.18

Answer: 3.07

5. 10.4 – 6.73

Answer: 3.67

6. 5.85 – 2.4

Answer: 3.45

7. 6.5 – 3.25

Answer: 3.25

8. 15.02 – 9.67

Answer: 5.35

9. 11.6 – 4.9

Answer: 6.7

10. 12.45 – 7.99

Answer: 4.46

Addition word problems (30 minutes) 

1. Shopping Problem

Emily bought a book for $12.75 and a pencil case for $3.50. How much did she spend in total?

Answer: 12.75 + 3.50 = 16.25

2. Distance Travelled

Sarah walked 3.6 miles to the park and then 2.8 miles to her friend's house. How many miles did Sarah walk in total?

Answer: 3.6 + 2.8 = 6.4 miles

3. Total Time Spent

John worked for 4.5 hours on Monday and 6.25 hours on Tuesday. How many hours did he work in total?

Answer: 4.5 + 6.25 = 10.75 hours

4. Total Cost

A sandwich costs $4.50, and a drink costs $2.80. What is the total cost of both items?

Answer: $4.50 + $2.80 = $7.30

5. Weight of Fruits

Anna bought 1.25 kg of apples and 2.75 kg of oranges. How much fruit did she buy in total?

Answer: 1.25 + 2.75 = 4.00 kg

Subtraction Word Problems: 25 mimin

1. Money Spent

Mary had ₹20. She bought a book for ₹7.50. How much money does she have left?

Answer: 20.00 – 7.50 = 12.50

2. Time Left

The movie started at 7:00 PM and ended at 9:15 PM. How long was the movie?

Answer: 9.15 – 7.00 = 2.15 hours (or 2 hours and 9 minutes)

3. Distance Remaining

Kevin ran 5.3 miles in the morning and 2.8 miles in the afternoon. How many miles does he have left to run if his goal is 10 miles?

Answer: 10.00 – (5.3 + 2.8) = 2.9 miles left

4. Weight Loss

Samantha started her diet weighing 160.5 pounds. After two weeks, she weighs 155.25 pounds. How much weight has she lost?

Answer: 160.5 – 155.25 = 5.25 pounds

5. Decimal Puzzle Match 15 min

Form students into teams of 5.

Activity: Prepare cards with problems on one card and answers on another. Mix them up, and students must match each problem to the correct answer.

Problems (cut these into individual cards):

1. 3.25 + 1.75        

2. 6.4 – 2.15

3. 5.85 + 4.15

4. 9.1 – 3.6

5. 7.35 + 2.65

6. 10.5 – 7.25

7. 8.75 + 1.25

8. 12.6 – 4.8

9. 2.5 + 5.5

10. 11.9 – 6.45

Answers (cut and mix up):

A. 5.00

B. 4.25

C. 6.15

D. 9.00

E. 7.7

F. 8.75

G. 7.50

H. 9.00

I. 3.25

J. 9.2

The first team to correct will win.

Expected learning outcome 

Knowledge Building:

• By the end of the lesson, students will be able to:
• Add and subtract decimal numbers accurately.
• Align decimals correctly.
• Solve real-life word problems involving decimals

Skills Building:

Problem-solving and self-checking