The average weight of a class of 24 students is 36 kg. When the weight of the…

Concept: When a new member joins a group, the new average equals the new total value divided by the new count. Equivalently, the new member's own value equals the new total minus the old total.

Working:

1. Total weight of the 24 students = 24 × 36 = 864 kg.

2. New average weight after the teacher joins (25 people) = 36 + 1 = 37 kg.

3. New total weight of all 25 people = 25 × 37 = 925 kg.

4. Teacher's weight = New total − Old total = 925 − 864 = 61 kg.

Check: Adding 61 kg to the students' total of 864 kg gives 925 kg; dividing by 25 people gives 37 kg, exactly 1 kg more than the original average of 36 kg — confirming the result.