Multiple choice

The mean age of $25$ students in a class is $12$. If the teacher's age is included, the mean age increases by $1$. Then teacher's age (in years) is:

  1. $24$
  2. $38$
  3. $30$
  4. $48$
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B Correct answer
Explanation

Sum of 25 students' ages = 25 * 12 = 300. With teacher, total people = 26, mean = 13. New sum = 26 * 13 = 338. Teacher's age = 338 - 300 = 38.

AI explanation

The total age of the 25 students is 25 multiplied by 12, which equals 300. When the teacher is included, the average age of 26 people becomes 13. The new total age is 26 multiplied by 13, equaling 338. The teacher's age is the difference between the new total and the old total: 338 minus 300 equals 38. The teacher's age is 38.

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