This is a
problem involving half-lives. We can solve this problem by using the equation
as shown: A=Aoe^-(ln2/t)T where A is the final amount (1.2milligram), Ao is
the initial amount (19.2mg), t is the half-life (4.5 days) and lastly T
time elapsed (required). Plug in the values in the equation and you should
get 18 days. Eighteen days have passed.
