I understand the concept of radioactive decay when you have only one element.
But what happens when one element decays into a second element and the second decays into a third. What is the quantity of not decayed material of the second element? And what if you have a longer chain? For example:
Element A has a half-life
Element B has a half-life
Element C is stable.
A decays to B which decays to C.
A(t), B(t), C(t) - is the quantity of A, B, C at time t