Question

A 15-g sample of radioactive iodine decays in such a way that the mass remaining after t days is given by m(t) = 15e^(−0.051t), where m(t) is measured in grams. After how many days is there only 3 g remaining?

Answer 1

Solve 3 = 15 e^(−0.051t) for t

0.2 = e^(−0.051t)

ln (0.2) = -1.609 = -0.051 t
t = 31.6 (days)