If one of the atoms is removed from a simple cubic unit cell the effective number of atoms remaining in a unit cell is

1. A simple cubic unit cell has atoms present at every corner of the cubic unit cell. The number of corners in a cubic unit cell = 8

2. Therefore, the contribution of each atom in a cubic unit cell is $\frac{1}{8}$

3. 1 atom is removed from the unit cell.

4. Therefore, the remaining atom in the cubic unit cell is $1-\frac{1}{8}=\frac{7}{8}atoms$