NUMBER · GRADE 6 · ALBERTAOUTCOME AB-MAT6-N3
L2 · Prime and composite numbers
Learning goal
“I can tell whether a number is prime or composite by counting its factors, and I know why 1 is neither prime nor composite.”
Prime number — a whole number with exactly two factors: 1 and itself. 7 is prime.
Composite number — a whole number with more than two factors. 8 has 1, 2, 4, 8: composite.
Square number — a number made by multiplying a whole number by itself, like 16 = 4 × 4. Its array is a perfect square.
Worked example
Sort 7 and 8. 7: factor pairs (1, 7) only — arrays: a 1-by-7 strip, or turned, 7-by-1, the same pair. Exactly two factors → 7 is prime. 8: factor pairs (1, 8), (2, 4) — four factors: 1, 2, 4, 8 → 8 is composite. Why it works: a prime number makes only one rectangle shape (the strip); a composite number makes at least one more shape.
Check yourself — explain it
Why is 1 not prime?
Paired problem — example still visible
Is 11 prime or composite? → Prime — pairs (1, 11) only, exactly two factors
Faded completion — last step is yours
“15: pairs are (1, 15) and (3, 5), so 15 has ___ factors and is ___.” → 4 factors; composite
Ready to practise?
10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.