SOLUTION: Can I just ask if 7 hours is a correct answer or nah? I'm kinda confused and is unsure of my process.Thank you. :) A drug is eliminated from the body through urine. Suppose that

Question 1095972: Can I just ask if 7 hours is a correct answer or nah? I'm kinda confused and is unsure of my process.Thank you. :)
A drug is eliminated from the body through urine. Suppose that for a dose of 10 milligrams, the amount A(t) remaining in the body t hours later is given by A(t)=10(0.8)^t and that in order for the drug to be effective, at least 2 milligrams must be in the body. Determine when 2 milligrams is left in the body.

Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
A(t)=10(0.8)^t; A(t) must be at least 2.
2=10(0.8)^t
2/10=0.8^t
0.2=0.8^t
take ln both sides
ln (0.2)=t ln (0.8) by property of logs
t=ln(0.2)/ln(0.8)
t=7.21 hours

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