Iodine 131 is a radioactive isotope. After 4.00 days, 70.8% of a sample of 131I remains.What is the half life of 131I?

Answer 1

.708=(0.5)^(4.00/half life)

Take log on both sides and rearrange equation to solve for half life.

-.150=(4.00/half life)*-.301
(4.00/half life)=.498
half life = 8.03 min

Answer 2

I might believe 8 days but not 8 min.