25 pupils sat for an English test. The average score of 20 of them was 80 marks. The total scores of the other 5 pupils was 350 marks. Find the average score of the 25 pupils.

Hi Xin, 
Please find below the solution to the asked query :

$$\begin{gathered} \mathrm{We} \mathrm{have}, \\ \mathrm{average} \mathrm{score} \mathrm{of} 20 \mathrm{pupils} = 80 \\ \Rightarrow \frac{\mathrm{Total} \mathrm{score} \mathrm{of} 20 \mathrm{pupils}}{20} = 80 \\ \Rightarrow \mathrm{Total} \mathrm{score} \mathrm{of} 20 \mathrm{pupils} = 1600 \\ \mathrm{Now}, \mathrm{total} \mathrm{score} \mathrm{of} \mathrm{remaining} 5 \mathrm{pupils} = 350 \\ \mathrm{So}, \mathrm{total} \mathrm{score} \mathrm{of} 25 \mathrm{pupils} = 1600 + 350 = 1950 \\ \mathrm{Now}, \mathrm{average} \mathrm{score} \mathrm{of} 25 \mathrm{pupils} = \frac{\mathrm{total} \mathrm{score} \mathrm{of} 25 \mathrm{pupils} }{25} = \frac{1950}{25} = 78 \end{gathered}$$

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