GRE quiz: Set problems

Of the 800 seniors at Kyrie University, 120 are pre-med, 120 are pre-law, and 20 are in both. How many seniors are neither pre-med nor pre-law?

A. 580
B. 660
C. 720
D. 800

Answer: A. 580

Learn how to solve this:
https://app.achievable.me/study/gre/learn/set-problems