Question

Which of the following are co-primes?
(a) 39, 91
(b) 161, 192
(c) 385, 462
(d) none of these

Answer 1

(b) 161 and 192

(a) 39 and 91 are not co-primes as 39 and 91 have a common factor, i.e. 13.
(b) 161 and 192 are co-primes as 161 and 192 have no common factor other than 1.
(c) 385 and 462 are not co-primes as 385 and 462 have common factors 7 and 11.