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Home  >>  JEEMAIN and AIPMT  >>  Mathematics  >>  Class11  >>  Statistics
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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

$\begin {array} {1 1} (A)\;40 & \quad (B)\;20 \\ (C)\;80 & \quad (D)\;60 \end {array}$

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Let the number of boys and girls be $x$ and $y$
$ \therefore 52x+42y=50(x+y)$
$ 52x+42y=50x+50y$
$ 52x-50x=50y-42y$
$ 2x=8y$
$ x = 4y$
Total number of students in the class = $ x+y$
$ = 4y+y$
$ = 5y$
Percentage of boys = $ \large\frac{4\not{y}}{\not{5}\not{y}} \times {\not100}^{20}$
$ = 80$
Ans : (C)
answered Jan 29, 2014 by thanvigandhi_1

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