A student's mark was wrongly entered as 83 instead of 63. Due to that the average marks for the class got increased by \(\dfrac12\). What is the number of students in the class?
Answer: B
Let the total number of students \(=x\)
The average marks increased by \(\dfrac12\) due to an increase of \(83 - 63 = 20\) marks.
But total increase in the marks
\(\dfrac{1}{2}\times x = \dfrac{x}{2}\)
Hence we can write as,
\(\dfrac{x}{2}=20\\
\Rightarrow x = 20 \times 2 = 40\)