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Q.
The average marks of boys in a class is $52$ and that of girls is $42$ The average marks of boys and girls combined is $50$ . The percentage of boys in the class is
Solution:
No. of boys & girls be $x \& y$
$52 x+42 y=50(x +y)$
$2 x=8 y$
$x=4 y \ldots \ldots(1)$
Total no. of students in a class $=x+y$
$=4 y+y = 5y$
% of boys $=\frac{4 y}{5 y} \times 100$
$=\frac{4}{5} \times 100=80$