Question

Which pair of numbers is relatively prime? A. 102 and 321 B. 10 and 45 C. 3 and 51 D. 35 and 72

Answer 1

Which pair of numbers is relatively prime?


D. 35 and 72

Answer 2

Okay. I will list all the relatively prime numbers up to 331.
2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101, 103,107,109,113,127,131,137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331.
Okay, so look at this list and see which match up. 
For A. 102 and 312. Neither of these numbers are relatively prime.
For B. 10 and 45. Neither of these are relatively prime. 
For C. 3 and 51. 3 is a relatively prime number, 51 is not. 
For D. 35 and 72. Neither of these are relatively prime numbers.
But the answer would be D. because to get a relatively prime pair of numbers you have to have both of them not be divisible by the same number. 102 and 312 can be divided 2, so that's not the answer. 10 and 45 can be divided by 5, so that is incorrect. 3 and 51 can be divided by 3, so that is also incorrect. 35 and 72 cannot be divided by the same numbers. 
So, the answer is D. 35 and 72.