Suppose we consider a large number of containers each containing initially 10000 atoms of a radioactive material with a half life of 1 yr. After 1 year,
none of the containers can have more than 5000 atoms.
All of these
all the contains will conatin the same number of atoms of the material but that number will only be approximately 5000
the containers will in general have different numbers of the atoms of the material but their average will be close to 5000
