The human resources department has classified all company employees according to highest level of education attained, and job classification. Education levels are high school, up to four years of post-secondary education, graduate degree, and post-graduate studies. Job classifications are clerical, professional, and managerial. The company has 37 managers, 10 of whom have either a graduate degree or post-graduate studies. None of these has only high school education. What is the probability that a randomly selected manager has up to four years of post-secondary education?