申論題

1.[30%] The daily concentration of pollutants in a river has a mean of 70 mg/ and a standard deviation of 10 mg/l.

(i) (10%) Suppose that the daily concentration follows a normal distribution. The critical level of pollutant concentration would be reached if the daily concentration exceeds 100 mgl. What is the probability that the daily concentration of pollutants in the river would not exceed the critical level?