The daily average concentration of pollutants in a stream follows a lognormal distribution with a mean of 60 mg/1 and a c. o.v. of 20%.What is the probability that the average concentration of pollutant in the stream will exceed 100 mg/l (a critical level) on a given day? Suppose the pollutant concentration between days are statistically independent. What is the probability that the critical level of pollutant concentration will not be reached during a given week?