The rockwell hardness of a metal is determined by impressing a hardened point into the surface of the metal and then measuring the depth of penetration of the point. suppose the rockwell hardness of a particular alloy is normally distributed with mean 68 and standard deviation 3. (rockwell hardness is measured on a continuous ) if a specimen is acceptable only if its hardness is between 67 and 75, what is the probability that a randomly chosen specimen has an acceptable hardness? (b) if the acceptable range of hardness is (70-c, 70+c), for what value of c would 95% of all specimens have acceptable hardness?