Question

Iodine-125 has a half-life of about 60 days.

Answer 1

the answer is 15.625mg

Answer 2

Since it has a half life of 60 days, this means that every 60 days it multiplies by 0.5. Since it asks for 300 days, your equation is 500*(0.5)^5, which is 15.625 mg left after 300 days.