The average age of 120 students in a group in 13.56 yrs, 35% of the number of students are girls and the rest are boys. If the ratio of the average age of boys and girls is 6 : 5, then what is the average age ( in yrs) of the girls?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is 4 i.e. 12
Total students = 120
No. of girls = 120 (35/100) = 42
No. of boys = 120 - 42 = 78
Total age of 120 student = 13.56 (120) = 1627.2
Let the average age of boys and girls be 6x & 5x
Total age of girls = 42(5x) = 210x
Total age of all boys = 78(6x) = 468x
Total age of 120 student = Total age of all girls + total age of all boys
1627.2 = 210x + 468x
x = 2.4
Average age of girls = 5x = 5 × 2.4 = 12