### A pupil’s marks were wrongly entered as 83 instead of 63. Due to that the average marks for the class got increased by half $\frac{1}{2}$ . The number of pupils in the class is:

A. 10

B. 20

C. 40

D. 73

$\begin{array}{l}\text{Let there be x pupils in the class}\\ \text{ Total increase in marks }\\ =x\times\frac{1}{2}=\frac{x}{2}\\ \therefore\frac{x}{2}=(83-63)\\ \Rightarrow\frac{x}{2}=20\\ \Rightarrow x=40\end{array}$