50 students surveyed about kind of peanut butter they like

Question

25 students prefer chunky (A) 20 students prefer smooth (smooth) B

13 prefer both

How many students prefer neither?

Answer 1

P(not(A or B)) = 1 - P(A or B) = 1 - (P(A) + P(B) - P(A and B)) = 1 - (25/50 + 20/50 - 13/50) = 1 - 32/50 = 18/50 = 9/25