Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)? How many will remain after two half-lives (60 seconds)? Three half-lives?

Question

So basically, after 30 seconds it will be 50.After 60 sec. 25 and after 90 sec. it will be 12.5...?
am I right?

Q2) Suppose you analyzed a sample of isotope A. It contained 25 radioactive isotope A atoms, and 103 stable daughter atoms. Approximately how old is the sample?