what are co primes

Co-prime numbers are two numbers that have no common factor other than 1. Their highest common factor (HCF/GCD) is 1.

Quick examples

• 4 and 9 are co-prime because their only common factor is 1.

• 5 and 7 are co-prime for the same reason.

• 8 and 12 are not co-prime because they share factors like 2 and 4.

Key point

• Co-prime numbers do not have to be prime themselves.
• For example, 4 and 9 are both composite, but they are still co-prime.

Easy way to check

1. Find the factors of both numbers.
2. See whether the only common factor is 1.
3. If yes, they are co-prime.

If you want, I can also give you a very short exam-style definition or a few practice questions.