Which pair of numbers does not have the HCF as 1?

a) 2 and 5  b) 3 and 5  c) 2 and 6  d) 6 and 7

Answer: option (c) - The HCF of 2 and 6  is not 1.

Explanation:

Let us find the HCF of each of the above options.

HCF of 2 and 5

HCF of 2 and 5 is 1

b) HCF of 3 and 5 

The highest common factor of 3 and 5  is 1

HCF of 3 and 5 is 1

c) HCF of 2 and 6

Common Factors of 2 and 6 : 1 and 2

The highest common factor is 2

 HCF of 2 and 6 is 2

d) HCF of 6 and 7

The only common factor of 6 and 7 is 1

Therefore, HCF of 6 and 7 is 1

Hence, the correct answer to our question is option (c) HCF of 2 and 6 is not 1 .