{Total} = {finance} + {marketing} - {both} + {neither}
100 = 25 + 50 - {both} + 40
{both} = 15%.
Walking across campus, a student interviewed a group of students. 25% of the students took a finance class last semester, 50% 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] 15%
[e] 10%