1. The problem is to understand the notation "X with a line on top," which typically represents the mean or average of a set of values denoted by $X$. 2. In statistics, the notation $\overline{X}$ (X with a line on top) is used to denote the sample mean, calculated as the sum of all sample values divided by the number of values. 3. Mathematically, if you have $n$ values $X_1, X_2, \ldots, X_n$, then the mean is given by: $$\overline{X} = \frac{1}{n} \sum_{i=1}^n X_i$$ 4. This formula means you add all the values $X_1$ through $X_n$ together and then divide by the total number of values $n$. 5. The mean is a measure of central tendency, giving a single value that summarizes the data set.