Since there 18 out of the 30 students chose Strawberry
12 did not choose Strawberry since 30 - 18 = 12
Too find the percentage, you take the amount of students that did not choose Strawberry, and divide it by the total number of students.
12 divided by 30 = 0.4
Multiply .4 by 100 and you'll get 40
So the answer is 40%