Question

The mass of the radioactive isotope sodium-24 in a sample is initially measured at 5 milligrams. If the mass of the sodium-24
decreases by 50% every 15 hours, what is the closest to the mass of the sodium- 24 in the sample 10 hours after the initial measurement?

Answer 1

m(t) = 5*(1/2)^(t/15). At t = 10 h:

m = 5*(1/2)^(10/15) = 5*2^(-2/3) ≈ 3.15 mg.

So about 3.15 milligrams.