Answer:
A score of 50 is a central score if it's close to the middle of the distribution. A score is considered extreme if it's above 2 or below -2. For example, if x=50, then:
z=(50-45)/10=0.5: is a central score.
z=(50-90)/20=-2: is an extreme score.
z=(50-60)/20=-0.5: is a central score.
A value is considered extreme if it's greater than the 95th percentile. A value greater than a Z-score of 3 is also considered extreme.