The gas phase reaction 2A ⇋ B is carried out in an isothermal plug flow reactor. The feed consists of 80 mole % A and 20 mole % inerts. If the conversion of A at the reactor exit is 50%, then $$frac{{{{text{C}}_{text{A}}}}}{{{{text{C}}_{{{text{A}}_{text{0}}}}}}}$$ at the outlet of the reactor is