20 vote
In an elementary school, the average age of students is 8 years and that of 12 teachers is 45 years. If the average age of all is 9 years, then what are the number of students?
In an elementary school, the average age of students is 8 years and that of 12 teachers is 45 years. If the average age of all is 9 years, then what are the number of students?
1). 432
2). 540
3). 408
4). 416
1 answers
30 vote
Let the number of students be ‘x’.
⇒ Sum of ages of all students/x = 8
⇒ Sum of ages of all students = 8x
Now, Sum of ages of teachers/12 = 45
⇒ Sum of ages of teachers = 540
Average of all;
⇒ (Sum of ages of students + Sum of ages of teachers)/(x + 12) = 9
⇒ 8x + 540 = 9x + 108
⇒ 9x – 8x = 540 – 108
⇒ x = 432
∴ Total number of students = x = 432
