A patient ingests 5 grams of a certain drug which dissolves away at a constant rate of 10% per hour. How long will it take before there is only one gram left?

Answer 1

P = Ae^rt where r= rate of decay and t = time measured in hours

P =Ae^-.10t

1 =5e^-1t divide by 5

1/5 = e^.-1t take natural logs of each side

ln(1/5) = -0.1t divide by -0.1

t = ln(1/5)/-0.1 = -1.609/-.1 = 16.09 hours until it decays from 5 grams to 1 gram