Class 8 Maths – Chapter 16: Playing with Numbers
Step 4: Prime, Composite & Co-prime Numbers
1️⃣ Prime Numbers
A prime number is a number greater than 1 which has exactly two factors: 1 and itself.
Examples: 2, 3, 5, 7, 11, 13
2️⃣ Composite Numbers
A composite number is a number greater than 1 which has more than two factors.
Examples: 4, 6, 8, 9, 10, 12
📌 Important Note
- 1 is neither prime nor composite
- 2 is the only even prime number
3️⃣ Co-prime Numbers
Two numbers are called co-prime if they have no common factor other than 1.
Examples:
- 8 and 15 ✔
- 9 and 10 ✔
- 12 and 18 ✘ (common factor = 6)
📘 Solved Examples
- Is 29 a prime number? → Yes (only factors 1 & 29)
- Is 21 composite? → Yes (factors: 1, 3, 7, 21)
- Are 14 and 25 co-prime? → Yes
📝 Exam Writing Tips
- Write definition clearly
- Mention factors step-by-step
- Underline final conclusion
🧠 Memory Tricks:
Prime → Only 2 friends (1 & itself)
Composite → Many friends
Co-prime → Only common friend is 1
📘 Class 8 Mathematics – Complete Library
CBSE | NCERT | State Syllabus
Chapter 1: Rational Numbers
Chapter 2: Linear Equations in One Variable
Chapter 3: Understanding Quadrilaterals
Chapter 4: Practical Geometry
Chapter 5: Data Handling
Chapter 6: Squares and Square Roots
Chapter 7: Cubes and Cube Roots
- NCERT Notes
- MCQs
- Worksheet
- Worksheet Answers
- Mind Map & Easy Tricks
- Important Exam Questions
- Very Important Questions
No comments:
Post a Comment