The effective number of atoms per unit cell of bcc arrangement of a metallic crystal is $\text{'}{Z}_1\text{'}$.  The effective number of atoms per unit cell of fcc arrangement of a metallic crystal is$\text{'}{Z}_2\text{'}$ .  Correct relation is  

$Z_1+Z_2\Rightarrow$Effective number of atoms per unit cell of hcp arrangement

$Z_1>Z_2\Rightarrow$Coordination number of metal in simple cubic arrangement

$\frac{Z_2}{Z_1}\Rightarrow$Coordination number of metal in simple cubic arrangement

$Z_1-Z_2\Rightarrow$Effective number of atoms per unit cell of simple cubic arrangement