Professor Sanchez has been teaching Principles of Economics for over 25 years. He uses the following scale for grading.
Let X X be a discrete random variable from a distribution with the probability mass function P (X = x) P ( X = x) , where P (X = x) P ( X = x) denotes the probability that X X takes the value x. x. Then, the cumulative distribution function is given by: P (X ≤ a) = ∑ x≤aP (X =x) P ( X ≤ a) = ∑ x ≤ a P ( X = x)