(a) If a single potassium measurement is made, what is the probability that Judy is diagnosed as hypokalemic? (b) If measurements are made instead on 4 separate days and the mean result is compared with the criterion 3.5, what is the probability that Judy is diagnosed as hypokalemic? S5.12 The level of nitrogen oxides (NOX) in the exhaust of a particular car model varies with mean 0.9 grams per mile (g/mi) and standard deviation 0.15 g/mi. A company has 125 cars of this model in its fleet. (a) What is the approximate distribution of the mean NOX emission level x for these cars? (b) What is the level L such that the probability that x is greater than L is only 0.01?