Question

Which pair of numbers is relatively prime?

O 7 and 21
O4 and 15
O 6 and 9
O9 and 27

Answer 1

Answer: 4 and 15 (choice B)

Reason:

Relatively prime numbers have a GCF of 1. The largest factor they have in common is 1. Another term for "relatively prime" is "coprime".

7 and 21 have a GCF of 7, which means they are not relatively prime. We can eliminate choice A off the list. Choice C and choice D are a similar situation.