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danlew
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The average age of students in class A is 15 years. What is the age of the only maths teacher in class A ?

\(Average = \frac{Sum}{Total Count}\)

1) There are 15 students in class A

15 * 15 = 225

We know total age of the class of students = 225

We cant determine the age of maths teacher from this.

Hence, (1) =====> is NOT SUFFICIENT

2) The average age of the students and the maths teacher in class A is 16 years

16 * 16 = 256

We now know the total age of the class along with the maths teacher

We still cant determine the age of maths teacher from this.

Hence, (2) =====> is NOT SUFFICIENT

Combining (1) & (2)

Age or maths teacher = 256 - 225 = 31

(1) & (2) =====> is SUFFICIENT

Hence, Answer is C
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danlew
The average age of students in class A is 15 years. What is the age of the only maths teacher in class A ?

1) There are 15 students in class A
2) The average age of the students and the maths teacher in class A is 16 years

Given : Avg. age of students = 15 and there is a maths teacher.
DS: Age of maths teacher

Option 1 : There are 15 students
So total weight = 15 *15 = 225, but no idea about maths teacher or avg. wt including maths teacher.
NOT SUFFICIENT

Option 2 : Avg. age of the students and the maths teacher = 16
But we don't know how many students are there to calculate the age of maths teacher.
NOT SUFFICIENT

Combined : Total age of students = 225
Total age of students + maths teacher = 16 * 16 = 256

age of maths teacher = 256 - 225 = 31.
SUFFICIENT

Answer C.
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