Question

the mean age of 25 students In a class is 12 the if the teachers age is included the mean age increased by 1 the teachers age in years

Answer 1

mean age of 25students is 12

sum of their ages = 25×12=300

now new mean is 13 and total people are 26

so sum of their ages=26×13=338

age of teacher =338-300=38 yrs

hope you got the answer

Answer 2

Mean = 12
No. of students = 25

$mean = \frac{sum \: of \: observations}{number \: of \: observations}$
$12 = \frac{sum}{25} \\ 12 \times 25 = sum \\ 300 = sum \\ \: sum \: of \: observations \: = 300$
If teacher's age is included,mean is increased by 1.
New Mean = 13
Let teacher's be x.
$mean = \frac{300 + x}{26} \\13 = \frac{300 + x}{26} \\ 13 \times 26 = 300 \times + x \\ 338 = 300 + x \\ x = 338 - 300 \\ x = 38$

Age of teacher is = 38 Years


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