Let atoms of $\mathrm{Y}$ in ccp structure $=100$

Then, number of tetrahedral voids $=2\times 100$

$\because$ Number of $\mathrm{X}$ atoms $=\frac{2}{3}$ rd of tetrahedral voids

$\therefore$ Number of $\mathrm{X}$ atoms $=\frac{2}{3}\times 200=\frac{400}{3}$

Hence, formula of compound can be $={\mathrm{X}}_4{\mathrm{Y}}_3$.