If the HCF of two numbers is 1, what could be the numbers? 

The Highest common factor of any set of numbers is the largest possible number which divides the given numbers exactly without any remainder.

Answer: If the HCF of two numbers is 1, the numbers are called co-prime numbers.

Lets see how to solve it.

Explanation:

If the HCF of two numbers is 1 that means there is no common factor except 1. Those types of numbers are called co-primes.

For example: (2,3), (3,5), (8,15), (10,33) etc;.

For the HCF to be 1, they themselves need not always be prime numbers, like for example (6,35) are coprime. Both 6 and 35 are composite numbers.

Therefore, If the HCF of two numbers is 1, the numbers are called co-prime numbers.