Factors & Primes

How it works

• 1A factor is a number that divides in exactly — nothing left over. 10 ÷ 2 = 5 exactly, so 2 is a factor of 10. But 10 ÷ 3 leaves a bit over, so 3 is not.
• 2Factors come in pairs that multiply back to the number: 1 × 10 and 2 × 5. So the factors of 10 are 1, 2, 5 and 10.
• 3A prime is a number that won't split into a times fact. Its only factors are 1 and itself. 7 is prime — nothing makes 7 except 1 × 7.
• 49 is not prime (3 × 3 = 9). 10 is not prime (2 × 5 = 10). 11 IS prime — try to split it, nothing works.
• 5Two traps: 1 is NOT prime (it only has one factor), and 2 is the only even prime.