Initially a gas of diatomic molecules is contained in a cylinder of volume `V_1` at a pressure `P_1` and temperature 250 K. Assuming that 25% of the molecules get dissociated causing a change in number of moles. The pressure of the resulting gas, at temperature 2000 K, when contained in a volume `2V_1` is given by `P_2`. The ratio `P_2//P_1` is ________.