Question

A 20.0 gram sample of a certain radioisotope decays over a
period of 19.2 hours. After that time, only 2.50 g of the isotope
remains. Calculate the half-life.

Answer 1

quantity of the substance remaining = initial quantity of the substance * (.5)^(time elapsed/half life of the substance)

2.50 = 20 * (.5)^(19.2/x)