The measure of data that must represent a number in the set that is greater than 2 of the numbers in the set and less than 2 of the numbers is the median.
The median is the middle value in a set of data when the values are listed in order from least to greatest (or greatest to least). If there are an odd number of values in the set, the median is the middle value. If there are an even number of values in the set, the median is the average of the two middle values.
If a number in the set is greater than 2 of the numbers and less than 2 of the numbers, then it falls between the first and last quartile of the data set. Therefore, the median, which represents the middle value in the data set, must also fall between the first and last quartile, and thus it must represent a number in the set that is greater than 2 of the numbers and less than 2 of the numbers.