The radioactive isotope you discovered at 8 a.m weighed 75 mg. You named it "Nerdium." At 3 p.m. it measured only 0.009 grams. What is its half-life?

Answer 1

using mg as the basis,

9 = 75*(1/2)^7x
x = 0.437 hrs

makes sense, since 9/75 is about 1/8 or 3 half-lives 3/7 =0.43