Introduction

Natural numbers are the set of positive integers starting from 1 and counting upwards infinitely. They are denoted by the symbol $\mathbb{N} = {1, 2, 3, 4, ...}$. In this topic, we will explore the properties and operations involving natural numbers.

Classification of Natural Numbers

Prime Numbers

• Prime numbers are natural numbers greater than 1 that are only divisible by 1 and themselves.
• Example: $2, 3, 5, 7, 11, ...$

Composite Numbers

• Composite numbers are natural numbers greater than 1 that have more than two factors.
• Example: $4, 6, 8, 9, 10, ...$

Even Numbers

• Even numbers are natural numbers that are divisible by 2.
• Example: $2, 4, 6, 8, 10, ...$

Odd Numbers

• Odd numbers are natural numbers that are not divisible by 2.
• Example: $1, 3, 5, 7, 9, ...$

Worked Example

Question: Determine whether 17 is a prime number.

Solution:

• We check if 17 has any factors other than 1 and 17.
• 17 is divisible only by 1 and 17, so it is a prime number.

Properties of Natural Numbers

Closure Property

• The sum or product of two natural numbers is also a natural number.
• Example: $3 + 4 = 7$, $2 \times 5 = 10$

Commutative Property

• The order of addition or multiplication of natural numbers does not affect the result.
• Example: $a + b = b + a$, $a \times b = b \times a$

Associative Property

• The grouping of natural numbers in addition or multiplication does not affect the result.
• Example: $(a + b) + c = a + (b + c)$, $(a \times b) \times c = a \times (b \times c)$

Identity Property

• The sum of any natural number and zero is the number itself.
• Example: $a + 0 = a$

Worked Example

Question: Simplify $7 + (3 \times 2)$.

Solution:

• Using the associative property, we first perform the multiplication.
• $7 + (3 \times 2) = 7 + 6 = 13$

Common Mistakes

• Confusing prime and composite numbers.
• Forgetting the order of operations in calculations.
• Misinterpreting the properties of natural numbers.

Key Points

• Natural numbers are positive integers starting from 1.
• Prime numbers have only two factors: 1 and the number itself.
• Composite numbers have more than two factors.
• Even numbers are divisible by 2, while odd numbers are not.
• Properties of natural numbers include closure, commutative, associative, and identity properties.

Practice Questions

1. Determine whether 29 is a prime number.
2. Calculate: $5 \times (2 + 4)$.
3. List the first four odd numbers.
4. Is 12 a composite number? Explain.
5. Evaluate: $9 + 3 \times 2$.

Practice Questions - Worked Answers

1. Solution: 29 is a prime number as it is only divisible by 1 and 29.
2. Solution: $5 \times (2 + 4) = 5 \times 6 = 30$.
3. Solution: The first four odd numbers are 1, 3, 5, 7.
4. Solution: Yes, 12 is a composite number as it has factors other than 1 and 12.
5. Solution: $9 + 3 \times 2 = 9 + 6 = 15$.