# A pupil’s marks were wrongly entered as 83 instead of 63…

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### 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:

1. A. 10
2. B. 20
3. C. 40
4. D. 73

eqalign{ & {text{Let}},{text{there}},{text{be}},x,{text{pupils}},{text{in}},{text{the}},{text{class}}{text{.}} cr & {text{Total}},{text{increase}},{text{in}},{text{marks}} cr & = {x times frac{1}{2}} = frac{x}{2} cr & therefore frac{x}{2} = left( {83 - 63} right) cr & Rightarrow frac{x}{2} = 20 cr & Rightarrow x = 40 cr}