A theoretical justification based on a certain material failure mechanism underlies the assumption that ductile strength of a material has a lognormal distribution. Suppose the values of the parameters are , = 5 and o = .1. a. What proportion of material specimens have ductile strength exceeding 120? What proportion have a ductile strength of at least 120? b. What proportion of material specimens have a ductile strength between 110 and 130? c. If the smallest 5% of strength values were unacceptable. what would be the minimum acceptable strength?