In many states it is illegal to drive with a blood alcohol level greater than 0.10% (one part alcohol per 1,000 parts blood) suppose someone who was involved in an automobile accident had blood alcohol tested at 0.20% at the time of the accident. Assume that the percentage of alcohol in the blood decreases exponentially at the rate of 10% per hour.
(a) Find the percentage of alcohol in the bloodstream at any value of time t.
(b) How long will i t be until this person can legally drive?