(B) Let the number of girls be $x$.Then,the number of boys is $(600 - x)$.The average age of the school is $11$ $years$ and $9$ $months$,which is equa

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(B) Let the number of girls be $x$.Then,the number of boys is $(600 - x)$.The average age of the school is $11$ $years$ and $9$ $months$,which is equal to $11 + \frac{9}{12} = 11 + \frac{3}{4} = \frac{47}{4}$ $years$.The total age of all students is the sum of the total age of boys and girls.$(600 - x) \times 12 + x \times 11 = 600 \times \frac{47}{4}$$7200 - 12x + 11x = 150 \times 47$$7200 - x = 7050$$x = 7200 - 7050 = 150$.Therefore,the number of girls in the school is $150$.

Competitive Quantitative Aptitude Average Average

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In a school with $600$ students,the average age of the boys is $12$ $years$ and that of the girls is $11$ $years$. If the average age of the school is $11$ $years$ and $9$ $months$,then the number of girls in the school is:

A
$450$
B
$150$
C
$250$
D
$350$

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In a school with $600$ students,the average age of the boys is $12$ $years$ and that of the girls is $11$ $years$. If the average age of the school is $11$ $years$ and $9$ $months$,then the number of girls in the school is:

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