When a non-volatile solute is added to the solvent, the vapour pressure of the solvent decreases by \( 10 \, \text{mm of Hg} \). The mole fraction of the solute in the solution is \( 0.2 \). What would be the mole fraction of the solvent if decreases in vapour pressure is \( 20 \, \text{mm of Hg} \)?