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Average age of class of 39 student is 15 years. If the age of teacher is included the average is increased by 3 months. Find the age of the teacher?

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Since Average age of class of 39 student is 15 years

and  the age of teacher is included the average is increased by 3 months

so average age after involving of teacher=15.25 years

now age of teacher=40*15.25-39*15

                              =610-585

                              =25 years
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Since the average age is 15 years for 39 students, we have,

(Sum of ages of all Students) / 39 =15

Sum of ages of all students = 39 * 15 = 585 years ......................... (1)

Once the age of the teacher is added, we have the average as

(Sum of ages of students + teacher's age) / (39+1) = 15.4

hence Sum of ages of students + teacher's age = 616 years..........(2)

Solving the above two equations,

Teacher's age = 616 - 585 = 31 years

 

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