Correct Option (3)
The average weight for the students of the class remains the same. This is because the students are merely reallocated among different groups (A, B, and C) within the same class. No students are added to or removed from the class. Consequently, the total number of students in the class remains constant, and the sum of the weights of all students in the class also remains unchanged. Since the class average weight is calculated by dividing the total weight of all students by the total number of students, and both these values are constant, the overall average weight of the class does not change.
Incorrect Options:
Options 1 (It increases) and 2 (It decreases) are incorrect because an increase or decrease in the average weight of the class would only occur if there was a change in the total weight of all students or the total number of students in the class. As explained, neither of these factors changes when students are simply shifted between internal groups.
Option 4 (No conclusion can be drawn due to insufficient data) is incorrect. While individual group averages might change, the question specifically asks about the average weight for the students of the class. Given that the total number of students and their combined total weight within the class remain constant, a definitive conclusion can be drawn regarding the class's overall average weight.