Given an alloy of Cu, Ag and Au in which Cu atoms constitute the CCP arrangement. If the hypothetical formula of the alloy is ${\mathrm{Cu}}_4{\mathrm{Ag}}_3\mathrm{Au}$. What are the probable locations of Ag and Au atoms?

There are 4 copper atoms per unit cell. As a result, 4 atoms make up the FCC arrangement, which equals the number of octahedral voids. Two tetrahedral voids are present. There are 24=8 octahedral voids. 

The given hypothetical formula is ${\mathrm{Cu}}_4{\mathrm{Ag}}_3\mathrm{Au}$.

This is possible if ${\left(\frac{1}{4}\right)}^{\text{th }}$of the octahedral voids and  ${\left(\frac{3}{2}\right)}^{\text{th }}$of the tetrahedral voids are occupied.