Posted by **Ralph** on Thursday, April 7, 2011 at 12:51am.

the concentration of a certain substance in our organism is given by the model Q9t) = Q(subscript 0) e^-0.1960t

a) what quantity of substance is present in the organism of this individual 3 hours after ingestion?

b) after how many hours will there only be 10% of this substance ingested by the individual?

- Math -
**MathMate**, Thursday, April 7, 2011 at 9:29am
Q(t) = Q_{0} e^-0.1960t

where t=elapsed time in hours (Check, not mentioned in the question).

So after three hours,

Q(3) = Q_{0} e^(-0.1960*3)=?

Q(t) = 0.9Q_{0}

or

e^(-0.1960t)=0.9

Take natural log:

-0.1960t = ln(0.9)

t=ln(0.9)/(-0.1960)=?

I'll leave it to you to work on your calculator.

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