In a particular class, 8 students have blue eyes, 13 have brown eyes, and 4 have green eyes. Round final answers to four decimal places as needed.

a. If two different students are randomly selected, what is the probability at least one student has green eyes?
b. If two different students are randomly selected, what is the probability neither have brown eyes?
c. If two different students are randomly selected, what is the probability they both have blue eyes?