Given numbers are 51 and 85

Now,

51 = 17 × 3

85 = 17 × 5

HCF = product of common factors with lowest power

⇒ HCF = 17

Hence, HCF of the given numbers is 17

Answer:

HCF = Highest common factor

factors of:-

51 :- 1, 3, 17, 51

85:- 1, 5, 17, 85

HCF = 17