math
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

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MathMate
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.
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