SOLUTION: ``A drug is eliminated from the body through urine. Suppose that for a dose of 200 milligrams, the amount remaining in the body 4 hours later is 100 milligrams: For the drug to

Question 1130838: ``A drug is eliminated from the body through urine. Suppose that for a dose of 200 milligrams, the amount remaining in the body 4 hours later is 100 milligrams:
For the drug to remain effective for the patient at least 40mg must remain in the body. With that in mind after how many hours should the patient be given the next dose?
Please show me how you got the answer, thank you.''.

Answer by josgarithmetic(39630) (Show Source): You can put this solution on YOUR website!
Description tells you that the half-life is 4 hours.

Without creating a function,

TIME(hours)      miligrams
0                 200
4                 100
8                  50
12                 25

40 milligrams would remain and new dose needed some time between 8 and 12 hours. Probably near about 9 hours.

Starting through this would help get a more accurate result:

Let y=40, take logs of both sides to solve for t:

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