We have the mean (m) 128.5 and the standard deviation (sd) 8.2, we must calculate the value of z for each one and determine whether or not it is an outlier:
z = (x - m) / sd
In the first case x = 148:
z = (148 - 128.5) /8.2
z = 2.37
In the second case x = 102:
z = (102 - 128.5) /8.2
z = -3.23
In the first case x = 152:
z = (152 - 128.5) /8.2
z = 2.86
The value of this is usually between -3 and 3, therefore when x is 102 it goes outside the range of the value of z, which means that this is the outlier.
