The professors at Acme University are required to submit their final exams to the registrar's office 10 days before the end of the semester. The exam coordinator received all 20 exams from the 20 professors on staff and recorded the number of days before the final exam that each submitted his or her exam. The results are:

15 8 3 2 6 4 10 13 15 12 7 3 9 13 15 8 11 12 4 1

a) What is the mean?

b) What is the median?

c) What is the mode?

d) Based in the values of the mean, median and mode, what is the most likely shape of the distribution?