Potassium level

Judy’s measured potassium level varies according to the Normal distribution with mean = 3.8 and standard deviation = .2. A patient is classified as hypokalemic if the potassium level is below 3.5.(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?