Mathematics for IGCSE & O level - Number (Section 1 - No. 2)

Identify a pair of numbers where their HCF is 1.

12 and 18

15 and 20

7 and 10

21 and 28

If two numbers have an HCF of 1, they are said to be relatively prime. 7 and 10 have an HCF of 1.