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Prime and Composite Numbers

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Prime or composite practice, factor pairs that decide it, a hundred chart activity that finds every prime to 100, and a printable prime numbers chart.

Download the prime and composite numbers worksheets

Prime or composite

Decide whether each number is prime or composite, and use factor pairs to show why.

Prime numbers to 100

Find the primes to 100 on a hundred chart by crossing out multiples, and a chart of all 25 primes.

Print at 100% (actual size) for the cleanest tracing lines.

About these prime and composite numbers worksheets

A prime number has exactly two factors: 1 and itself. 7 is prime because the only way to make 7 is 1 × 7. A composite number has more than two factors: 12 is composite because 12 = 1 × 12 = 2 × 6 = 3 × 4. The number 1 is neither prime nor composite, because it has only one factor.

There are 25 prime numbers up to 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97. Only one of them, 2, is even. The hundred chart page lets children find all of them themselves by crossing out the multiples of 2, 3, 5 and 7, which is far more memorable than reading a list.

The practice pages mix in composites that look prime, like 51 (3 × 17), 87 (3 × 29) and 91 (7 × 13), so children check for factors instead of guessing from the last digit.

Standards

  • CCSS.MATH.CONTENT.4.OA.B.4Find all factor pairs for a whole number in the range 1–100. Recognize that a whole number is a multiple of each of its factors. Determine whether a given whole number in the range 1–100 is a multiple of a given one-digit number. Determine whether a given whole number in the range 1–100 is prime or composite.

How to use them

  1. Start with Factor Pairs: Prime or Composite? Listing the pairs makes the definition concrete.
  2. Do Find the Prime Numbers to 100 as a class or in pairs, then compare with the prime numbers chart.
  3. Use Prime or Composite? for quick practice once children know how to check.
  4. Keep the prime numbers chart in a folder for reference.

Teaching tips

  • To test a number to 100, try dividing by 2, 3, 5 and 7. If none of them divides it evenly, it is prime.
  • Every even number except 2 is composite.
  • 1 is neither prime nor composite.
  • Watch for numbers like 51, 57, 87 and 91: they look prime but are not.

Questions teachers and parents ask

What is a prime number?

A whole number greater than 1 with exactly two factors, 1 and itself. 2, 3, 5, 7 and 11 are the first five.

Is 1 a prime number?

No. 1 has only one factor, so it is neither prime nor composite.

How many prime numbers are there up to 100?

There are 25 prime numbers from 1 to 100.

Is 2 a prime number?

Yes. 2 is the only even prime number. Every other even number has 2 as a factor, so it is composite.