The mean age of 30 student is 9 years. If the age of their teacher is included, it becomes 10 years. The age of teacher ( in years ) is

27

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31

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35

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40

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Solution

The correct option is D $40$
Given:Average age of $30$ students $= 9$ years.
Total age of $30$ students $= 9 \times 30 = 270$ years.
Teacher's age included.
So, average age of $30$ students $+$ one teacher $= 10$ years.
$\Rightarrow$ Total age of $30$ students $+$ one teacher $= 10 \times 31 = 310$ years.
$∴$ age of teacher $= 310 - 270 = 40$ years.

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The mean age of 30 student is 9 years. If the age of their teacher is included, it becomes 10 years. The age of teacher ( in years ) is

The correct option is D 40Given:Average age of 30 students=9years.Total age of 30 students=9×30=270 years.Teacher's age included.So, average age of 30 students+one teacher=10years.⇒Total age of 30 students + one teacher=10×31=310 years.∴ age of teacher=310−270=40 years.