posted by lily .
After several drinks, a person has a blood alcohol level of 220 mg/dL (milligrams per deciliter). If the amount of alcohol in the blood decays exponentially, with one fourth being removed every hour, find the person's blood alcohol level after 4 hours
Work with what's left, i.e. r=3/4.
Over 4 hours, fraction left
x = (3/4)^4=0.3164
Level = 220 mg/dL * x = 69.6 mg/dL.