Question

Doctors use iodine-131 to treat some forms of cancer. The half-life of iodine-131 is 8 days. A patient receives a treatment of 12 millicuries. A millicurie is a unit of radioactivity. How much iodine-131 remains in the patient 16 days later?

Answer 1

I know the answer is 3, but I want to use a function, since it is the main focus of the lesson. I having trouble setting up a function.

Answer 2

if the half life is 8 days, 1/2 is gone every 8 days. so after 8 days it is 1/2, 16 days is 1/4...

so at 16 days it is 12 x 1/4 = 3 mc

Answer 3

Another way to solve it is:

amount = 12 (1/2)^(168)
= 12(1/2)^2 = 3 millicuries

Answer 4

How did you get 168?

Answer 5

And how did you get 2?

Answer 6

That was a typo. She meant 16/8
since that is how many half-lives there were.

Answer 7

Oh, that makes more sense. Thanks, Elina and Steve!