SOLUTION: Hospitals use radioactive substance iodine-131 in their researches.A hospital purchased 40 grams of the substance.Eight days later,when a doctor wanted to use some of the iodine-13

Question 632073: Hospitals use radioactive substance iodine-131 in their researches.A hospital purchased 40 grams of the substance.Eight days later,when a doctor wanted to use some of the iodine-131,he found out that only 20 grams remained.Predict the amount remaining two weeks after purchase.
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
Hospitals use radioactive substance iodine-131 in their researches.A hospital purchased 40 grams of the substance.Eight days later,when a doctor wanted to use some of the iodine-131,he found out that only 20 grams remained.Predict the amount remaining two weeks after purchase.
A = Pe^(kt)
determine exponential decay constant k:
20 = 40e^(k*8)
.5 = e^(k*8)
ln(.5) = k*8
ln(.5)/8 = k
.
Our equation is now:
A = 40e^(t*ln(.5)/8)
.
Now we can answer:Predict the amount remaining two weeks after purchase.
two weeks is equivalent to 14 days:
thus t =14
A = 40e^(t*ln(.5)/8)
A = 40e^(14*ln(.5)/8)
A = 40e^(-1.213)
A = 11.89 grams

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