What is the average (arithmetic mean) age of all students in the city'

Mean age = Total Sum of ages of all the students in all the schools / Total number of students

1.) Sum of ages of students in one school / number of students in that school = 12
=> Sum of ages of students in one school = 12 * (number of students in that school )
Similarly,
Sum of ages of students in second school / number of students in that school = 12
=> Sum of ages of students in Second school = 12 * (number of students in that school )

Adding all these,

Sum of ages of all students in all schools = 12 * (total number of students)
=> Mean age = 12
Sufficient
2.) only gives, number of students in each school. in sufficient

ans A

Yeah, the answer is A. Thank you very much for explanations. But I thought this question can not be so easy. While reading choice 1 at first, I remembered that term "average" applies to mean, median and mode. And thus, I picked answer E, because of this uncertainty...going crazy with GMAT

Let there be 2 schools A and B
To find. Mean age = sum of ages of students in A and B / sum of number of students in A and B
= age A + age B/ no. A + no. B

1. The average age of the students in each of the city's schools is 12.
We have two schools A and B.
For A.
Avg1 = sum of ages of student in school A/ no. of student in school A
12 = sum of ages of student in school A/ no. of student in school A

sum of ages of student in school A = 12 * no. of student in school A

Avg2=sum of ages of student in school B/ no. of student in school B
12 = sum of ages of student in school B/ no. of student in school B

sum of ages of student in school B = 12 * no. of student in school B

Mean Age=sum of ages of student in school A+sum of ages of student in school B /no. of student in school A+ no. of student in school B
= 12 * no. of student in school A + 12 * no. of student in school B/no. of student in school A+ no. of student in school B
=12(no. of student in school A + no. of student in school B)/no. of student in school A+ no. of student in school B
=12.

Sufficient.

2. The number of students in each of the city's schools is 70.
Mean Age=sum of ages of student in school A+sum of ages of student in school B /no. of student in school A+ no. of student in school B
= sum of ages of student in school A+sum of ages of student in school B /70+70
=sum of ages of student in school A+sum of ages of student in school B /140.

sum of ages of student in school A+sum of ages of student in school B --we do not know this.

Insufficient.

OA A.

A


1 is enough as if the average of all the schools are 12 means then mean is also 12

What a question ! :D

if average age of students at each school is 12.. that means..mean of every school will be ..

for example..there are 5 schools...(12,12,12,12,12) there means will be 12..
Ans is A..

statement 2..is insufficient..

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