In a certain faculty of science, 70% of students studied physics, 50% studied chemistry, 40% studied biology, 30% studied physics and chemistry, 30% studied chemistry and biology, while 20% studied physics and biology. If a student is to be selected at random, what is the probability that the student studied.
a.) all the three subjects
b.) physics and biology but not chemistry
c.) show that the probability of students that studied physics and chemistry is 30%
