Learning Objectives
By the end of this lesson, you will be able to:
- Add decimals to hundredths (Objectives 82, 87)
- Subtract decimals to hundredths (Objectives 82, 87)
- Multiply decimals by whole numbers (Objectives 83-84)
- Divide decimals by whole numbers (Objectives 85-86)
- Solve word problems involving decimal operations
SEA Tip
Decimal operations appear in Section I, II, and III of the SEA Math paper. These are essential for money and measurement! (SEA Framework Page 21-22)
Watch: Adding Decimals
Start by watching this video to learn how to add decimals. Take notes as you watch! 📝
Adding Decimals – Mathematics Video Lesson
Quick Check
Did you understand the video? Review the notes below before continuing! ✅
Adding & Subtracting Decimals
Adding and subtracting decimals is similar to whole numbers. The KEY is to LINE UP THE DECIMAL POINTS!
Rules for Adding & Subtracting Decimals
- Line up the decimal points vertically
- Add zeros to make the same number of decimal places
- Add or subtract as you would with whole numbers
- Bring down the decimal point to your answer
📊 Example 1: Adding Decimals
3.45 + 2.7 = ?
Solution:
- Line up decimals:
- 3.45
- + 2.70 (add zero to match places)
- Add: 3.45 + 2.70 = 6.15
Answer: 6.15
📊 Example 2: Subtracting Decimals
5.8 − 2.35 = ?
Solution:
- Line up decimals:
- 5.80 (add zero to match places)
- − 2.35
- Subtract: 5.80 − 2.35 = 3.45
Answer: 3.45
Common Mistake
Never forget to line up the decimal points! This is the most important step in decimal addition and subtraction.
Watch: Subtracting Decimals
Now watch this video to learn how to subtract decimals. Pay attention to borrowing! 🎯
Subtracting Decimals – Mathematics Video Lesson
Watch: Multiplying Decimals
Watch this video to learn how to multiply decimals by whole numbers. 🎯
Multiplying Decimals – Mathematics Video Lesson
Multiplying Decimals
Multiplying decimals is different from adding. You DON’T line up the decimal points!
Rules for Multiplying Decimals
- Multiply as if they were whole numbers (ignore decimals)
- Count the total decimal places in both numbers
- Place the decimal in the answer (same number of places from the right)
📊 Example 3: Multiplying Decimals
2.5 × 3 = ?
Solution:
- Multiply as whole numbers: 25 × 3 = 75
- Count decimal places: 2.5 has 1 decimal place
- Place decimal: 7.5 (1 place from right)
Answer: 7.5
📊 Example 4: Multiplying Decimals
1.25 × 4 = ?
Solution:
- Multiply as whole numbers: 125 × 4 = 500
- Count decimal places: 1.25 has 2 decimal places
- Place decimal: 5.00 = 5 (2 places from right)
Answer: 5
Watch: Dividing Decimals
Watch this video to learn how to divide decimals by whole numbers. 🎯
Dividing Decimals – Mathematics Video Lesson
Dividing Decimals
Dividing decimals by whole numbers is straightforward. Keep the decimal point in line!
Rules for Dividing Decimals
- Set up the division problem normally
- Bring up the decimal point to the quotient (answer)
- Divide as you would with whole numbers
- Add zeros if needed to continue dividing
📊 Example 5: Dividing Decimals
4.8 ÷ 2 = ?
Solution:
- Set up: 2 ⟌ 4.8
- Bring up decimal: Place decimal in answer directly above
- Divide: 4 ÷ 2 = 2, 8 ÷ 2 = 4
- Answer: 2.4
Answer: 2.4
📊 Example 6: Dividing Decimals
7.5 ÷ 3 = ?
Solution:
- Set up: 3 ⟌ 7.5
- Bring up decimal: Place decimal in answer
- Divide: 7 ÷ 3 = 2 R1, bring down 5, 15 ÷ 3 = 5
- Answer: 2.5
Answer: 2.5
Memory Trick
Add/Subtract: LINE UP the decimals
Multiply: COUNT the decimal places
Divide: BRING UP the decimal
Lesson Complete!
Great job finishing Lesson 1.14! You’re mastering decimal operations for the SEA exam! 🎉
Back to SEA Maths