Radioactive substances are eradicated from living organisms by two procedures: natural physical decay and biological metabolism. Every process contributes to the effective half-life E which is defined by 1/E = 1/P + 1/B, where P is physical half-life of radioactive substance and B is biological half-life. (a) Radioactive iodine, I-131, is utilized to treat hyperthyroidism (overactive thyroid). It is assumed that for human thyroids, P = 8 days and B = 24 days. Determine effective half-life of I-131. days (b) Assume amount of I-131 in human thyroid after t days is modeled by A(t) = A0ekt, k < 0. Use effective half-life found in part (a) to find out percentage of radioactive iodine remaining in human thyroid gland five weeks after its ingestion.