Number properties

Questions on odd and even, primes, factors, multiples, divisibility and remainders. Testing small numbers is often the fastest proof.

1. When a question says "must be true," try a few numbers, including 0, 1, negatives and fractions if allowed.
2. For "divisible by both a and b," use the least common multiple.
3. Odd × odd = odd; anything × even = even; odd + odd = even.

• Multiplying the two numbers instead of finding the least common multiple.
• Forgetting that 1 is not prime and 2 is the only even prime.

Every practice question comes with a full explanation, including why each wrong choice is wrong. Free, with no account.