Hello there!
To find the mean of a data set, add all the values together and divide by the number of values in the set.
So we have
3, -10, -2, 13, 11,
Mean = [tex] \frac{3+(-10)+(-2)+13+11}{5}
[/tex]
Mean = 3 - 10 - 2 + 13 + 11/15
Mean = 15/5
Mean= 3
I hope this helps!