OG 2018 (DS #395)- confusing answer explanation

Are all of the numbers in a certain list of 15 numbers equal? 1. The sum of all the numbers in the list is 60. 2. The sum of any 3 numbers in the list is 12. I understand that Statement 1 is insufficient. If the sum of all the numbers in the list of 15 numbers is 60, and each number is equal to 4, t...