Posted by Misty on .
A sample has a mean of M = 25. If one person with a score of X = 25 is added to the sample, what effect will it have on the sample mean?
Why and how is there no effect on the sample mean? I am not really understanding this?

Math Statistics 
Ms. Sue,
Study this explanation of mean. The answer should be clear to you then.
http://www.mathsisfun.com/mean.html 
Math Statistics 
PsyDAG,
The mean functions as a fulcrum/balance point for the distribution. Since the score is added at the balance point, the mean does not change.