Iwas wondering if anyone could me solve this undergraduate level optimization problem.
prove that a concave function which is bounded from below in a polyhedron attains its minimum at one of the extremal points.

Peter applied to an accounting firm and a consulting firm. he knows that 30% of similarly qualified applicants receive job offers from the accounting firm, while only 20% of similarly qualified applicants receive job offers from the consulting firm. assume that receiving an offer from one firm is independent of receiving an offer from the other. what is the probability that both firms offer peter a job?