In a school of 600 students, the average age of boys is 12 years and that of the girls is 11 years. If the average age of all the students of the school is 11 years 9 months, then the number of girls in the school is ?
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The total number of girls in school is 150.
Total number of students in school = 600 (Given)
Average age of all students = 11 yrs 9 mnths (Given)
Average age of boys is 12 years (Given)
Average age of girls = 11 years (Given)
Let the number of girls be = x
Total age of girls = 11x --- equation 1
Number of boys = 600-x
Total age of boys = 12 ( 600-x) --- equation 2
= 11 × 9/12 = 47/4 yr
Therefore, total age of all the students -
= 600 × 47/4 = 7050 ---equation 3
From equation 1, 2 and 3
11x + 12 ( 600-x) = 7050
11x + 7200 - 12x = 7050
11x-12x = 7050 - 7200
-x = - 150
x = 150
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