Question 841973
Decay Equation in general, {{{A=Ie^(-kt)}}}.
A = amount after time t
I = initial amount when t=0
k = a constant
At half-life, {{{(1/2)=e^(-kt)}}} and you would want to find k for a given or known t.
{{{ln(1/2)=-kt}}}
{{{k=-(ln(1/2))/t}}}


You are given that t=120 for the half life and so you can calculate and find the value for k.