The grains composing polycrystalline metals tend to have weights that follow a log-normal distribution. For a type of aluminum, gram weights have a log-normal distribution with ? = 3 and ? = 4 (in units of 10-2g).
a. Find the mean and variance of the grain weights.
b. What is the probability that the grain weights will lay 2 standard deviations from the mean?
c. Find the probability that a randomly chosen grain weighs less than the mean grain weight.