Lesson 1 of 4 · Grade 5 Mathematics
Factors, multiples and prime numbers
15 min
Factors
Factors of a number divide it exactly with no remainder.
Factors of 12: 1, 2, 3, 4, 6, 12.
Multiples
Multiples of a number are got by multiplying it by 1, 2, 3, ...
Multiples of 4: 4, 8, 12, 16, 20, ...
Prime numbers
A prime number has exactly two factors: 1 and itself.
Prime numbers below 20: 2, 3, 5, 7, 11, 13, 17, 19.
- 1 is not prime (it has only one factor).
- 2 is the only even prime number.
Composite numbers
A composite number has more than two factors, for example 4, 6, 8, 9, 10, 12.
Divisibility tests
- By 2: the last digit is even.
- By 5: the last digit is 0 or 5.
- By 10: the last digit is 0.
- By 3: the sum of the digits is divisible by 3. Example: 123 → 1 + 2 + 3 = 6, so 123 is divisible by 3.
Key points to remember
- Factors divide a number exactly
- Multiples come from multiplying
- Primes have exactly two factors
- 2 is the only even prime; 1 is not prime
Test yourself
