Question 973319
C-11 retains 96.5% per minute.
If initial quantity is 1 unit, then 1 minute passing,
{{{0.965=1*e^(k*1)}}}

{{{ln(0.965)=k}}}, and computing this, 
{{{k=-0.03563}}}


The decay equation is  {{{A=A[o]e^(-0.03563t)}}}.




HALF-LIFE


Let {{{A=1/2}}}  and {{{A[o]=1}}}, and solve for t.