Lesson 2: Positive and Negative Integers – Addition, Subtraction, Multiplication, Division

📚 Introduction

Have you ever heard someone say, “The temperature is -3°C today!” 🥶 or “I owe you ₵10”? Those are examples of negative numbers — numbers less than zero!

In this lesson, you will learn how to work with positive and negative integers — adding, subtracting, multiplying, and dividing them confidently.

Don’t worry — with simple rules and lots of practice, you’ll be a master in no time! 🚀

🧠 Key Concepts and Explanations

1. What Are Integers?

Integers are whole numbers that can be positive, negative, or zero.

2. Adding Integers ➕

Rule:

• Same signs: Add the numbers and keep the sign.
• Different signs: Subtract and keep the sign of the bigger number.

Formula Examples:

Sample Walkthrough

Find: (-8) + (+5)

• Signs are different → subtract 8 – 5 = 3
• Keep the sign of the bigger number (8 is negative) → Answer = -3 ✅

3. Subtracting Integers ➖

Rule: Change subtraction to addition, then follow the addition rules!

Tip: Change the sign of the second number and add!

Formula Examples:

Sample Walkthrough

Find: (-10) – (-4)

• Change to addition: (-10) + (+4)
• Different signs → 10 – 4 = 6
• Keep the sign of the bigger number (10 is negative) → Answer = -6 ✅

4. Multiplying Integers ✖️

Rule:

• Same signs → Positive answer
• Different signs → Negative answer

Formula Examples:

Sample Walkthrough

Find: (-9) × (+7)

• Different signs → Negative answer
• 9 × 7 = 63

Answer: -63 ✅

5. Dividing Integers ➗

Rule: Same rules as multiplication!

Formula Examples:

Sample Walkthrough

Find: (+30) ÷ (-5)

• Different signs → Negative answer
• 30 ÷ 5 = 6

Answer: -6 ✅

📈 Useful Quick-Reference Table

📝 Practice Exercises

A. Add or Subtract

1. (-7) + (+2) = ______
2. (+5) – (-3) = ______
3. (-8) – (+6) = ______
4. (+10) + (-12) = ______

B. Multiply or Divide

1. (-6) × (-9) = ______
2. (+14) × (-3) = ______
3. (-42) ÷ (+6) = ______
4. (-24) ÷ (-8) = ______

C. Word Problems

1. The temperature was -5°C. It dropped by 7°C. What is the new temperature?
2. A diver is at -20 metres underwater and goes up 12 metres. Where is he now?

✅ Answers and Explanations

Add or Subtract

1. -5
2. 8
3. -14
4. -2

Multiply or Divide

1. 54
2. -42
3. -7
4. 3

Word Problems

1. -5°C – 7°C = -12°C
2. -20 + 12 = -8 metres

🔄 Recap

Today you learned that integers can be positive or negative, and that addition, subtraction, multiplication, and division have simple sign rules. Always watch the signs carefully! 👀

💬 Reflection

Imagine you are playing a video game where losing lives shows as -5 and gaining lives as +3. How would you calculate your total lives? 🎮