the average marks of 39 students of a class are 50 the marks obtained by XL student are 39 more than the average marks of all the students find mean marks of all the 40 students
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Let the marks scored by 40th student be x
So the average would become
(1950 + x)/40
Given that his marks are 39 more than the average of 40 students
=> x = (1950 + x)/40 + 39
=>
x = \frac{1950 + x}{40} + 39 \\ \\ = > x = \frac{1950 + x}{40} + \frac{1560}{40} \\ \\ = > x = \frac{3510 + x}{40} \\ \\ = > x = \frac{3510}{40} + \frac{x}{40} \\ \\ = > x - \frac{x}{40} = \frac{3510}{40} \\ \\ = > \frac{40x - x}{40} = \frac{3510}{40} \\ \\ = > \frac{39x}{40} = \frac{3510}{40} \\ \\ = > x = \frac{3510}{40} \times \frac{40}{39} \\ \\ = > x = 90
So the boy scored 90 marks
So average =
\frac{1950 + 90}{40} \\ \\ = \frac{2040}{40} \\ \\ = 51
The average is 51
Answer :- 51
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