Multiple choice

What is the age of class teacher? I. There are 11 students in the class. II. The average age of students and class teacher is 14 years. III. The average age of students and teacher is 3 years more than the average age of the students.

  1. I and III

  2. I and II

  3. II and either I or III

  4. All

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let average age of 11 students be S. Total students age = 11S. From III: (11S+T)/12 = S+3, so 11S+T = 12S+36, giving T = S+36. From II: (11S+T)/12 = 14, so 11S+T = 168. Substituting T: 11S+(S+36) = 168, so 12S = 132, S = 11. Therefore T = 11+36 = 47 years. All three statements are needed.

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