The equilibrium constants ${\mathrm{K}}_{{\mathrm{P}}_1}$  and ${\mathrm{K}}_{{\mathrm{P}}_2}$ for the reactions X  $\rightleftharpoons$ 2Y and Z $\rightleftharpoons$  P + Q, respectively, are in the ratio of 1 : 9. If the degree of dissociation of X and Z be equal, then the ratio of total pressures at these equilibria is