Logical Reasoning

Step 1: Understanding the Question:
The question asks to estimate the typical distribution of staff in a standard three-tier corporate pyramid.

Step 2: Detailed Explanation:
In most organizational structures, the number of employees increases as you go down the hierarchy levels.
Typically:
1. Top level (CEO/Executives): Very few ((<) 5%)
2. Middle level (Managers): Significant number (approx 20-40%)
3. Bottom level (Entry-level workers): The largest group.
In a basic balanced pyramid model used for logic puzzles, the entry-level group often accounts for roughly 50% or 1/2 of the total workforce to maintain a standard span of control for management.

Step 3: Final Answer:
In a standard hierarchy, entry-level employees make up approximately 1/2 of the total staff.