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

Question

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

p0sitr0n · Answer

you can do this intuitively. half life means that after that much time, only half of the mass remains. so after 8 days, 6 mc remain, and after 16 days 3 ms remain.