A 15-g sample of radioactive iodine decays in such a way that the mass remaining

Algebra
Tutor: None Selected Time limit: 1 Day

A 15-g sample of radioactive iodine decays in such a way that the mass remaining after t days is given by 

m(t) = 15e0.079t,
 where 
m(t)
 is measured in grams. After how many days is there only 5 g remaining? (Round your answer to the nearest whole number.)
 days
Jul 16th, 2015

Thank you for the opportunity to help you with your question!

5 = 15exp(-0.079t)

exp(-0.079t) = 5/15=1/3

-0.079t = ln(1/3)

t = - ln(1/3)/0.079

= 13.906 days

Hence, 5 gm will remain after 13.906 days.

Please let me know if you need any clarification. I'm always happy to answer your questions.
Jul 16th, 2015

We can say t = 14 days.

Jul 16th, 2015

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Jul 16th, 2015
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