Potassium - 42 is a radioisotope that nutritionists use to determine whether the body is effectively using potassium at the cellular level.
The half-life of potassium-42 is 12.4 hours. Assuming that a patient's cells assimilate all the potassium chloride tagged with potassium-42, approximately what percentage of the dose remains in 2.1 days? __________ .