Multiple choice

The average age of a class of $39$ students is $15$ years. If the age of the teacher is included, then the average increases by $3$ months. Find the age of the teacher.

  1. $30$
  2. $35$
  3. $25$
  4. $20$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total age of 39 students = 39 * 15 = 585. New average = 15 years + 3 months = 15.25 years. Total age with teacher = 40 * 15.25 = 610. Teacher's age = 610 - 585 = 25.

AI explanation

The total age of the 39 students is 39 times 15, giving 585 years. The new average age with the teacher is 15 years and 3 months, which is 15.25 years. This makes the total age of the 40 people equal to 40 times 15.25, which is 610 years. The teacher's age is the difference between 610 and 585, which is 25 years.

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