Judy's doctor is concerned that she may have hypokalemia (low potassium in the blood, measured in millimoles per liter, mmol/l). There is variation both in the actual potassium level and in the blood test that measures the level. Judy's measured potassium level varies according to the Normal distribution with =3.8 mmol/l and =0.2 mmol/l. A patient is classified as hypokalemic if the potassium level is less than 3.5 mmol/l.

If measurements are made on four separate days and the mean result is compared with the criterion 3.5 mmol/l, what is the probability that Judy is diagnosed as hypokalemic? (Enter your answer rounded to four decimal places.)