Answer
The mean will decrease
Explanation
An outlier is an observation that lies an abnormal distance from other values in a dataset. In the case of the dataset:
4, 5, 5, 6, 7, 8, 17
the outlier is 17
The mean is calculated as follows:
Then, the mean of the original dataset is:
After 17 is removed from the set, the mean is:
The mean will decrease if the outlier is removed