First let us define what an outlier is:
A value that "lies outside" (is much smaller or larger than) most of the other values in a set of data.
21, 13, 13, 37, 13, 23, 25, 15
Rearranging the data in ascending order,
13, 13, 13, 15, 21, 23, 25, 37
As we can see 37 is the outlier here as it way too bigger than other numbers.
<u><em>Calculating mean with the outlier:</em></u>
mean is found using the formula:
number of data values= 8
sum of data values = 13+13+13+15+21+23+25+37=160
Mean = 160/8 = 20
With the outlier mean is 20.
<em><u>Calculating mean without outlier:</u></em>
Number of data values = 7
sum of data values = 13+13+13+15+21+23+25=123
Mean = 123 /7 = 17.57
Mean without outlier is 17.57