Multiple choice

The average age of 39 students and the principal is 18 years. When the principal's age is excluded, the average age decreases by 1 year. What is the age of principal?

  1. 57 years

  2. 60 years

  3. 58 years

  4. 48 years
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A Correct answer
Explanation

Total of 40 people (39 students + principal) have average age 18, so sum = 40 × 18 = 720 years. When principal is excluded, 39 students have average 17, so their sum = 39 × 17 = 663 years. Principal's age = 720 - 663 = 57 years. This works because removing the principal reduces the average by exactly 1 year.

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