Gujarati
Hindi
4.Average
medium

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

$350$

Solution

Number of girls $=x$

Number of boys $=600-x$

$\therefore \quad(600-x) \times 12+11 x$

$=11 \frac{3}{4} \times 600=\frac{47}{4} \times 600$

$\Rightarrow 7200-12 x+11 x=7050$

$\Rightarrow \quad x=7200-7050=150$

Std 13
Quantitative Aptitude

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