Teacher’s weight from a slight average increase: The average weight of 40 students is 40 kg. Including the teacher increases the average by 0.5 kg. What is the teacher’s weight?

Introduction / Context:
A small change in average across many people implies a significant change in total weight. Use totals before and after including the teacher to isolate their weight.

Given Data / Assumptions:

• Students: 40 with average 40 kg.
• With teacher: 41 persons with average 40.5 kg.

Concept / Approach:
Compute totals from averages. Teacher’s weight = new total − old total.

Step-by-Step Solution:

Verification / Alternative check:
Check average difference: 0.5 * 41 = 20.5 extra total. Students at 1600; adding a 60.5 kg teacher indeed gives +60.5, which results in +0.5 average across 41.

Why Other Options Are Wrong:

• 40.5 kg: Too light; would hardly change average.
• 60 kg or 62 kg: Do not match the exact totals.

Common Pitfalls:
Using 40 (not 41) when multiplying the increased average or forgetting that the count changes to 41.

Final Answer: