Calculate the packing effeciency of a fcc crystal in which all the tetrahedral and octahedral voids are occupied by the largest spheres without disturibing the lattice.

Explanation

To calculate the packing efficiency of a face-centered cubic (FCC) crystal where all tetrahedral and octahedral voids are occupied by the largest spheres, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure:**
- In an FCC unit cell, there are 4 atoms per unit cell.

2. **Count the Voids:**
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