Question 957506
"The formula" might be P=Ie^(-kt) where I is the initial percent of polonium.  What is not clear is your description for half-life.  40 WHAT?


Half-life of polonium 210 is 138.4 days.  What is the unit of "40"?  This is unclear.


Ordinarily, advice would be use half-life information to find the k value, and then solve the question part of the problem  using this k value.


{{{highlight(P=Ie^(-kt))}}}
{{{ln(P)=ln(I)-kt}}}
{{{ln(P/I)=-kt}}}
{{{highlight_green(k=ln(I/P)/t)}}}