Use the graph below to answer the following questions. Assume one atom produces one count per minute. 

 

1. a. How many atoms are in the original sample size of this radioisotope?
2. 
   b. How long is the half-life in days?
3. 
   c. How many atoms are left after 2 half-lives?
4. 
   d. Approximately how many days would have to pass for there to be only 2.5 atoms of the sample remaining?