CO-PRIME NUMBERS

If the highest common factor (HCF) of two numbers is 1, then the numbers are said to be co-primes or relatively prime or mutually prime.

In other words, if two numbers do not have common divisor other than 1, they are said to be co-primes.

Here, the two numbers can both be primes as (3, 11) or both can be composites as (16, 35) or one can be a prime and other a composite as (7, 14).

Examples : 

Find which of the following pairs of numbers are co-primes. 

1)  4 and 12.

The above two numbers have the common divisors other than 1. They are 2 and 4. 

So, 4 and 12 are not co-primes. 

2)  7 and 43. 

The above two numbers have no common divisor other than 1.  

So, 7 and 43 are co-primes. 

3)  5 and 3. 

The above two numbers have no common divisor other than 1.  

So, 5 and 3 are co-primes. 

4)  8 and 17. 

The above two numbers have no common divisor other than 1.  

So, 8 and 17 are co-primes. 

5)  8 and 15. 

The above two numbers have no common divisor other than 1.   

So, 8 and 15 are co-primes. 

6)  14 and 21. 

The above two numbers have common divisor other than 1. That is 7.

So, 14 and 21 are not co-primes. 

7)  2 and 4. 

The above two numbers have common divisor other than 1. That is 2.   

So, 2 and 4 are not co-primes. 

8)  1 and 2. 

The above two numbers have no common divisor other than 1.   

So, 1 and 2 are co-primes. 

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