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 that the hardness of a particular alloy is normally distributed with a mean of 70 and standard deviation of 3 a)-consider the case where the specimen is only acceptable for hardness between 65 hardness? what range about the mean gives a probability of 95%? the range should be at is the probability that a randomly chosen specimen has an acceptable b)-symmetric about the mean.