A uniform square plate has a small piece QQ of an irregular shape removed and glued to the center of the plate leaving a hole behind in the figure. Then the moment of inertia about the z-z-axis is:
                    

1. increased
2. decreased
3. the same
4. changed in an unpredictable manner
Hint: The moment of inertia depends on mass distribution.

Explanation: In the given diagrams, when the small piece QQ is removed and glued to the center of the plate, the mass comes closer to the z-z-axis, hence, the moment of inertia decreases. Therefore, the moment of inertia about the z-z-axis is decreased.
Hence, option (2) is the correct answer.