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1. 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

Solution:

\begin{aligned} Let there be x pupils in the class . \\ Total increase in marks \\ = x \times \frac{1}{2} = \frac{x}{2} \\ ∴ \frac{x}{2} = (83 - 63) \\ \Rightarrow \frac{x}{2} = 20 \\ \Rightarrow x = 40 \end{aligned}

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