There are three Grade 1 classes in a small community. Mr. Smithers' class has 12 students in it, Ms. Ruffle's class has 16 students, and Ms. Peter's class has 10 students. Suppose 2 students are selected at random from the 38 Grade 1 students in this community.
a) What is the probability that the two selected students are not from the same class?
b) If you know that at least one of the selected students was from Ms. Ruffle's class, what is the probability they both were?