Let $A$ be a commutative ring (not necessarily noetherian). Let $I\subseteq J\subseteq A\,$ be two finitely generated ideals. Let us denote the completion functor by $\Lambda_K (M) = \varprojlim_n M/K^nM$. I would like to compare the two rings: $\Lambda_J(A)$ and $\Lambda_{J'} (\Lambda_I(A))$ where $J' = J\Lambda_I(A)$. Are they the same? are they isomorphic? I thought about showing that in the right hand side, $A$ is dense in the $J$-adic topology, and that it is $J$-adically complete. Is this true? and are those two facts enough to show that it is isomorphic to the left hand side?