HCF of two positive numbers are said to be 1 ,then the numbers are called as​

The numbers are called Co-prime or Relatively Prime numbers.

Here's why:

The Highest Common Factor (HCF) or Greatest Common Divisor (GCD) of two numbers is the largest number that divides both of them without leaving a remainder.

If the HCF of two numbers is 1, it means that there is no other number (except 1) that can divide both numbers exactly. In other words, the two numbers do not have any common factor other than 1.

Such numbers are called Co-prime or Relatively Prime numbers.

For example, 15 and 28 are co-prime numbers because the only number that can divide both of them exactly is 1.