The mean practice exercises

The problem

A high school teacher gave a history exam to her class of ten students. She graded the papers and recorded the score of each student. She then decided to calculate the mean of these scores.

$X$
19
20
18
13
16
17
20
28
16
18

To calculate the mean we add up all the scores and divide by the number of scores. Here is the formula for the mean.
$$\bar{X} ={\sum{X} \over {n}}$$ $$mean={sum of scores \over number of scores}$$

The solution

....next