The average age of 40 students and their class teacher is 16 years. If the teacher's age is left out, the average falls by 0.5 years. How old is the teacher?

20.5 yearsCorrect answerYour answer35.5 yearsCorrect answerYour answer36 yearsCorrect answerYour answer36.5 yearsCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

Total age with the teacher = $41 \times 16 = 656$ years.
Without the teacher the average is 15.5, so the students total $40 \times 15.5 = 620$ years.
Teacher's age = $656 - 620 = 36$ years.

Worth noting

Shortcut: teacher = $15.5 + 41 \times 0.5 = 36$ . Starting from 16 instead of 15.5 gives 36.5 years.

Ten questions from Averages, at your own pace.

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