NIMCET 2014 Question Paper with solutions

Given, combined average of class is 50. Let number of boys in class be x and number of girls in class be y By combined average formula
50 = $\frac{52\times \mathit{x}+42\times \mathit{y}}{\mathit{x}+\mathit{y}}$
⇒ 50x + 50y= 52x + 42 y
⇒ 8y = 2x
⇒ $\frac{\mathit{x}}{\mathit{y}}$ = $\frac{4}{1}$
⇒ $\frac{\mathit{x}}{\mathit{x}+\mathit{y}}$ = $\frac{4}{5}$
Hence, ratio of boys to total number of students is $\frac{4}{5}$ and percentage = $\frac{4}{5}$ × 100 = 80%