Which pair of numbers is relatively prime

a. 57 and 96
b. 68 and 118
c. 70 and 195
d. 143 and 323

Without any calculations it's evident it can't be neither B (both numbers are even, so they're divisible by 2) nor C (the numbers end in 0 and 5, so they're divisible by 5).

A.

Both numbers have a factor of 3, so they're not relatively prime.
That means it must be D. But, let's check it.



Indeed, those two numbers are relatively prime.