Stephanie surveyed a total of 25 students. 9 of them chose blue as a favorite color, and 16 did not. We will focus on those that did not choose blue as a favorite color.
16 out of 25 students did not choose blue as their favorite color. Divide 25 into 16:

Multiply this decimal by 100 to find the percentage:
64% of students did not choose blue as their favorite color.