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4th grade · Math · Unit 12 of 15

Prime & Composite

Count factors to sort numbers into prime and composite

What your child practices

A prime number has exactly two factors, 1 and itself (like 7). A composite number has more than two (like 12). 1 is neither. Children find factors with multiplication and division facts.

Alaska content standards learning standard: 4.OA.4 · finding factor pairs and telling prime from composite numbers

How we explain it

Children can open this short lesson before they practice.

  1. A factor divides a number with none left over.
  2. A prime number has exactly 2 factors: 1 and itself.
  3. A composite number has more than 2 factors.

Example: Is 22 prime or composite? 22 ÷ 2 = 11, so 2 is a factor. It has more than 2 factors. Answer: Composite

Prime & Composite in Alaska

In the Alaska content standards, this is unit 12 of 15 in 4th grade Math, after Metric Measures and before Feet, Pounds & Gallons.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alaska Department of Education and Early Development

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Which number is a factor of 38?

    • 36
    • 19
    • 24
    • 18

  2. Question 2

    Which is the only even prime number?

    • 2
    • 8
    • 6
    • 4

  3. Question 3

    Which number is composite?

    • 7
    • 21
    • 31
    • 11

  4. Question 4

    How many factors does 12 have?

    • 11
    • 6
    • 8

  5. Question 5

    Which number is prime?

    • 27
    • 39
    • 3
    • 9

  6. Question 6

    Is 45 prime or composite?

    • neither prime nor composite
    • prime
    • composite

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