Answer : Option B
Explanation :
$MF#%\begin{align}
&\text{Let the total number of students = x}\\\\
&\text{The average marks increased by }\dfrac{1}{2}\text{ due to an increase of 83-63=20 marks.}\\\\
&\text{But total increase in the marks = }\dfrac{1}{2}\times x = \dfrac{x}{2}\\\\
&\text{Hence we can write as}\\\\
&\dfrac{x}{2}=20\\\\
&\Rightarrow x = 20 \times 2 = 40
\end{align}$MF#%
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