Number Properties
Know primes, factors, multiples and the rules for odd and even numbers.
The rules
- The factors of a number divide it evenly. Multiples are what you get by multiplying it.
- LCM is the smallest shared multiple. GCF is the largest shared factor.
- Even × anything is even. Odd × odd is odd. Odd + odd is even.
- A prime has exactly two factors, 1 and itself. Note that 2 is the only even prime.
Watch out: Calling 1 prime. It has only one factor.
Worked example
What is the least common multiple of 12 and 18?
- 12 = 2²·3 and 18 = 2·3².
- Take the highest power of each prime: 2²·3² = 36.
Answer: 36
Try it yourself
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