Outliers are unusual values that can change the average (mean) and the middle value (median) when analyzing data.

1. Mean: To find the mean, you add up all the numbers and then divide by how many numbers there are. Outliers can make this average look different than what most of the data shows.

   • Example: If we look at the numbers {2, 3, 4, 5, 100}, the mean is calculated like this:
     [ \text{Mean} = \frac{2 + 3 + 4 + 5 + 100}{5} = 22.8 ]
     This number doesn't really show what most values are like because of the outlier (100).

2. Median: The median is the middle number in a sorted list. It isn’t affected as much by outliers.

   • Example: For the same group of numbers {2, 3, 4, 5, 100}, the median is (4). This value represents the usual data better.

In short, outliers can really change the mean, but the median stays more reliable.