{Total} = {finance} + {marketing} - {both} + {neither}
100 = 25 + 55 - {both} + 40
{both} = 20%.
Walking across campus, a student interviewed a group of students. 25% of the students took a finance class last semester, 55% took a marketing class last semester, and 40% took neither a finance nor a marketing class last semester. What percent of the students in the group took both a finance and a marketing class?
a: 60%
b: 50%
c: 25%
d: 20%
e: 10%