Question about Averages (Kizzy Reem's Question on Facebook)

[Sudharaka]

Kizzy Reem on Facebook writes:

If the mean average for 24 students is 78% and another student got 67% what is the mean average for the 25 students?

 

[Sudharaka]

Kizzy Reem on Facebook writes:

If the mean average for 24 students is 78% and another student got 67% what is the mean average for the 25 students?

Hi Kizzy,

Let \(x_{i}\) be the marks of the \(i^{th}\) student. Then the mean value of marks for 24 students is,

\[M_{24}=\frac{1}{24}\sum^{24}_{i=1} x_{i}=78\]

\[\Rightarrow \sum^{24}_{i=1} x_{i}=78\times 24~~~~~~~~~~(1)\]

Since the 25th student got 67% marks,

\[M_{25}=\frac{1}{25}\left(67+\sum^{24}_{i=1} x_{i}\right)~~~~~~~~(2)\]

Using (1) and (2) you'll be able to calculate \(M_{25}\).