Prime or composite

7th class prime or composite by Delta publications

Key Notes:

What is a prime number?

A prime number is a positive whole number with only two factors: 1 and itself.

For example, 7 is a prime number. The only factors of 7 are 1 and 7.

  • 1×7=7
What is a composite number?

A composite number has more factors than just 1 and itself.

For example, 15 is a composite number. It has factors 1, 3, 5, and 15.

  • 3×5=15
  • 1×15=15
Prime vs. Composite: A Quick Comparison
Prime Numbers
Only divisible by 1 and itself.
Have exactly two factors.
Examples: 2, 3, 5, 7, 11		Composite Numbers
Divisible by 1, itself, and at least one other number.
Have more than two factors.
Examples: 4, 6, 8, 9, 10
Prime and composite numbers chart

This chart shows all of the prime numbers within 200.

A chart with the numbers from two through two hundred is shown. The numbers two, three, five, seven, eleven, thirteen, seventeen, nineteen, twenty-three, twenty-nine, thirty-one, thirty-seven, forty-one, forty-three, forty-seven, fifty-three, fifty-nine, sixty-one, sixty-seven, seventy-one, seventy-three, seventy-nine, eighty-three, eighty-nine, ninety-seven, one hundred one, one hundred three, one hundred seven, one hundred nine, one hundred thirteen, one hundred twenty-seven, one hundred thirty-one, one hundred thirty-seven, one hundred thirty-nine, one hundred forty-nine, one hundred fifty-one, one hundred fifty-seven, one hundred sixty-three, one hundred sixty-seven, one hundred seventy-three, one hundred seventy-nine, one hundred eighty-one, one hundred ninety-one, one hundred ninety-three, one hundred ninety-seven, and one hundred ninety-nine are highlighted to show that they are prime numbers.
Identifying Prime and Composite Numbers: Some Tips
  • Check for divisibility by small prime numbers: Start by checking if the number is divisible by 2, 3, 5, or 7. If it is, it’s composite (unless the number is 2, 3, 5, or 7).
  • Even numbers greater than 2 are always composite: This is because they are divisible by 2.
  • Numbers ending in 0 or 5 are usually composite: This is because they are divisible by 5 (with the exception of 5 itself).
  • Practice makes perfect! The more you work with numbers, the easier it will become to recognize prime and composite numbers.
Why are Prime and Composite Numbers Important?

Prime and composite numbers are the fundamental building blocks of all whole numbers. Understanding them is crucial for many mathematical concepts, including:

  • Factoring
  • Simplifying Fractions
  • Finding the Greatest Common Factor (GCF)
  • Finding the Least Common Multiple (LCM)

Learn with an example

Is 7 a prime number or a composite number?

  • prime number
  • composite number

The only factors of 7 are 1 and 7.
7 is a prime number.

Is 20 a prime number or a composite number?

  • prime number
  • composite number

20 has more factors than just 1 and itself.
For example, 2 is a factor of 20:

20 ÷ 2 = 10
20 is not a prime number.

Is 13 a prime number or a composite number?

  • prime number
  • composite number

The only factors of 13 are 1 and 13.
13 is a prime number.

Let’s practice!✒️