Nuclide half-life?

Question

A 50 mg sample of a radioactive nuclide is administered to a patient to obtain an image of her thyroid.

If the nuclide has a half-life of 12 hours, how much of the nuclide remains in the patient after 5.0 days? 

Answer 1

FR = 0.5ⁿ

FR = fraction remaining = ?

n = number of half lives that have elapsed = 5 days x 24 hrs / day = 120 hrs x 1 half life / 12 hrs = 10

FR = 0.5¹⁰

FR = 0.000977 This is the fraction that remains after 5 days