aman gupta wrote on Nov 1st, 2012, 10:03am:So in the given circuit the RO of the first stage should become the RS for the second stage
What means "should become"? You are not allowed to take this resistor into consideration twice.
Let me explain again:
The gain of the 1st stage is calculated assuming it would be a stand-alone stage with an external load (input impedance of the 2nd stage).
The corresponding output voltage of the 1st stage act as the input voltage for the 2nd stage (assuming it would be an IDEAL source, because you have considered the output impedance for the 1st stage already during the first calculation).
This approach is in full agreement with the Substitution Theorem which provides the theoretical basis.
This theorem in short:
In an electrical network (linear or non-linear) you can replace each single node voltage or each single path current by an ideal voltage source resp. an ideal current source of the same value without influence on all other node voltages/path currents. OK? Further questions?