SOLUTION: The function f(x)= 40(0.8)^x gives the amount of a medication in milligrams present in a patient's system x hours after taking a 40-mg dose. In how many hours will there be less th

Question 447792: The function f(x)= 40(0.8)^x gives the amount of a medication in milligrams present in a patient's system x hours after taking a 40-mg dose. In how many hours will there be less than 2 mg of the drug in a patient's system?
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
The function f(x)= 40(0.8)^x gives the amount of a medication in milligrams present in a patient's system x hours after taking a 40-mg dose. In how many hours will there be less than 2 mg of the drug in a patient's system?
.
set f(x) to 2 and solve for x:

take log base .8 of both sides:

change of base:

answer:
more than 13.43 hours
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