Measures of Central 
           Tendency
    Measure of central tendency – A value that represents the 
    centre of a data set, can be the mean, median or mode.
     
    Data Set – A collection of numbers
    Ex:   [9,13,12,8,8] is a data set
                              Mean
        The “mean” is computed by adding all of the numbers in 
        the data together and dividing by the number of elements 
        contained in the data set.
        Example:
        Data Set =     2, 5, 9, 3, 5, 4, 7
        Number of Elements in Data Set =
        Mean = 
            Median
    The “median” of the data set depends on whether the 
    number of elements in the data set is odd or even.  Steps 
    to find the median:
    1. Reorder the data set from smallest to largest.
    2. If the number of elements is odd the median is the 
     middle number.
    3. If the number of elements is even the median is the 
     average of the two middle numbers.
                            Median
        Example #1:                     Example #2:
        Find the median of the          Find the median of the 
        data set:                       data set:
             9,13,12,8,8                     6,2,7,19,13, 9
                                         
        Written in increasing           Written in increasing 
        order =                         order = 
        8, 8, 9, 12, 13                 2, 6, 7, 9, 13, 19
        Median = 9                      Median =
                                        (7+9) ÷ 2 = 8
             Mode
  The mode for a data set is the element that occurs the most 
  often.  It is not uncommon for a data set to have more than one 
  mode.  Some sets have no mode.
      Example #1:
         [9,13,12,8,8]
          Mode = 8
      Example #2:
         [6,2,7,19,13, 9]
          Mode = no mode
     
      Example #3:
        [2,2,6,8,7,9,8]
          Mode = 2 and 8