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The mean age of a class of twenty students is 12. If their teacher's age is inclu...


Question

The mean age of a class of twenty students is 12. If their teacher's age is included, the mean becomes 13. The age of the teacher is

Options

A) 33

B) 39

C) 28

D) 25

The correct answer is A.

Explanation:

Total age of 20 students = \(12 \times 20 = 240\)
Age of teacher = \(x\)
\(\cfrac{x + 240}{21} = 13\)
\(x + 240 = 13 \times 21\)
\(x + 240 = 273\)
\(x = 273 - 240\)
\(x = 33\)
Teacher's age = 33 years

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Dicussion (1)

  • Total age of 20 students = \(12 \times 20 = 240\)
    Age of teacher = \(x\)
    \(\cfrac{x + 240}{21} = 13\)
    \(x + 240 = 13 \times 21\)
    \(x + 240 = 273\)
    \(x = 273 - 240\)
    \(x = 33\)
    Teacher's age = 33 years

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