Tetra-Ratio !!!!!

In a close packed atom lattice, the no. of atoms in a unit cell are $8$ at the corners and $6$ at the faces (Considering FCC lattice).

Every atom at the corner is shared by $8$ unit cells, so, total number of complete atoms is $8*1/8 = 1$ . Also, each face is shared by 2 unit cells, so total number of complete atoms is $6*1/2 = 3$ . So, total number of atoms is $1+3=4$

Now, since there are 2 tetrahedral void (or hole) at every body diagonal of the lattice...and since, there are 4 body diagonals, so total number of tetrahedral voids is $8$ . And since each void belongs to 1 unit cell, total number of tetrahedral voids is also $8$

So, the ratio is $4:8 = 1:2$