Question

A professor has recorded exam grades for 10 students in his class, but one of the grades is no longer redable.if the mean score on the exam was 80 and the mean of the 9 readable scores is 84, what is the value of the unreadable score.

Answer 1

We have The mean of a data-set is given by the sum of all values in the data-set divided by the number of values, so:

data set has 10 values

mean data set is 80

The 9 readable scores have a mean of 84, this is: 9 x 84 = 756

the value of the unreadable score is x

Therefore, the mean is:

$\frac{756+x}{10}=80$

then solve for x:

$\begin{gathered} 10\times\frac{756+x}{10}=80\times10 \\ 756+x=800 \\ 756+x-756=800-756 \\ x=44 \end{gathered}$

Answer: the value of unreadable score is 44