Question

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?

Answer 1

Study this explanation of mean. The answer should be clear to you then.

http://www.mathsisfun.com/mean.html

Answer 2

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.