Virginia SOL Math / Grade 5 / Number & Number Sense

5.NS.2

Prime, Composite & Prime Factorization

What you'll learn

  • Identify prime and composite numbers
  • Find the prime factorization of a whole number
  • Use factors and multiples to describe numbers

Words to know

Factor —
a whole number that divides another number evenly
Prime number —
a number with exactly two factors, 1 and itself
Composite number —
a number with more than two factors
Prime factorization —
a number written as a product of prime numbers
Factor tree —
a diagram that breaks a number into its prime factors

Why it matters Breaking numbers into prime factors helps us simplify fractions and find common factors and multiples.

Worked examples

Model ItI do

Is 17 prime or composite?

List the factors of 17. Only 1 and 17 divide it evenly, so it has exactly two factors. That means 17 is a prime number.

Try It TogetherWe do

Find the prime factorization of 24.

Break 24 into 4 times 6, then 4 into 2 times 2 and 6 into 2 times 3. The prime factors are 2, 2, 2, and 3, so 24 = 2 x 2 x 2 x 3.

Now YouYou do

Find the prime factorization of 36.

Use a factor tree until every branch ends in a prime. Check your answer in the back of this chapter.

Practice

Mastered 0 of 11

Warm-up

Ease in with the basics.

  1. 1.Is 2 prime or composite?

  2. 2.List all the factors of 6.

  3. 3.Is 9 prime or composite?

On Level

The core Quick Check from the book.

  1. 1.Is 29 prime or composite?

  2. 2.Is 21 prime or composite?

  3. 3.List all the factors of 18.

  4. 4.Write the prime factorization of 20.

  5. 5.Name one prime number between 40 and 50.

Challenge

Stretch your thinking.

  1. 1.Write the prime factorization of 72.

  2. 2.Write the prime factorization of 100.

  3. 3.List all the prime numbers between 30 and 40.