Question

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.
The number of pupils in the class are:

a) 10 b) 20
c) 40 d) 73

I only require the solution and not the answer...
Please help me with this...

Answer 1

Let n = number of pupils
Let x = incorrect average marks
Incorrect total marks = x * n
Corrected total marks = (x * n) - (83 - 63) = nx - 20 .................(1)
Also the correct total marks = (x - 0.5)n = nx - 0.5n .................(2)
Therefore nx - 20 = nx - 0.5n..................(3)

Now just solve (3) to find n

Answer 2

-20 = -0.5n

n = 20/0.5 = 40...

Answer 3

Okay, thanks buddy....

Answer 4

You're welcome :)