Average

The average of a data set is also known as the arithmetic mean.

The mean is equal to the sum of all the data points divided by the number of data points in the set. 

How Does It Appear on the Tests

• Mean-Median Comparison: Many ACT questions about the mean of a data set will ask students to compare the mean and the median: which is larger/smaller or are they the same? Data sets with numbers that are close to one another in value will have similar or identical means and medians. Data sets with more variation (or that are skewed in one direction or another) will have more distance between the mean and median.
• Individual Data Point Changes: Questions may also ask: how does increasing or decreasing one of the data points in the set change our mean? What data points would need to be added to get the mean to a particular value?  
• Calculating Mean from a Table or Graph: Can you calculate the mean of a data set from its histogram? A table of values?