After how many days are there only 5 g remaining?

Question

A 15 g sample of radioactive iodine decays in such a way that the mass remaining after t days is given by
m(t) = 15e^−0.087t, where m(t) is measured in grams.

Answer 1

m(t) = 15e^−0.087t

 

We want m(t) = 5 grams:

 

5 = 15e^−0.087t

(1/3) = e^−0.087t

ln(1/3) = −0.087t

ln(1/3)/(-0.087) = t days

 

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