find the equation

Question

Physicians use gallium citrate-67 to detect certain types of cancer, including lymphoma. Gallium citrate-67 has an effective half-life of 3.24 days—some is lost to radioactive decay, and some is removed through the digestive and urinary tracts. A patient who is breast-feeding is injected with the radioactive element. 

Let 

 be the percentage of the gallium citrate-67 that remains in the patient’s body at days since she was injected. Find an equation of f.

f(t)=

A scan of the gallium citrate-67 is performed 2 days after the injection. What percentage of the element remains? 

____%.  Round to 2 decimal places.

The patient can resume breast-feeding when only 0.39% of the gallium citrate-67 remains. When can she resume breast-feeding?

_____days Round to 1 decimal place.

Answer 1

I think the equation you are looking for is f(t) = f(0)*exp(-t ln 2/t_1/2)

where exp is the exponential function e^x and t_1/2 is the half-life in days.

This should allow you to answer the questions.