The chapter we are on is Radioactive Decay and the Nucleus. Here is the question:

There are 600 g of radioactive iodine-133. The half life of iodine-133 is 21 h.

a) How much of this radioactive substance would exist after 21 h. ?

b) After 42 h. ?

c) After 126 h. ?

P.S. If you could explain how to do this and maybe show me how to work this problem out, I would appreciate it!

- Confused