Question

In an exam, the average mark of the students of a class
was 20. But as the marks of '2' students were wrongly
recorded as 70 and 85 instead of 60 and 77, the actual
average would be 2 marks less. Find the number of
students who wrote the exam.​

Answer 1

Step-by-step explanation:

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Initial Average of marks = 45

Initial sum of marks = 45×30 = 1350

After correction marks of one increased by 45 and other decreased by 15. Hence, the new sum of marks =1350+45−15=1380.

New average =

$\huge{\underline{\red{\mathrm{Answer}}}}$

1380/30 = 46.

Answer 2

Answer:

Average * no. of students = total numbers

20(x-2) + 60 + 77

= 20x - 40 + 137

= 20x + 97

And,

18(x-2) + 70 + 85

= 18x - 36 + 155

= 18x + 119

Now, equate the equation

$20x + 97 = 18x + 119 \\ 2x = 22 \\ x = 11$

No. of Student = 11.