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This Java applet shows how the relationship between the mean and the median
and illustrates several aspects of these measures of central tendency.
The applet begins by showing a histogram
of 9 numbers. As can be seen in the histogram, the numbers are: 3, 4, 4, 5,
5, 5, 6, 6, and 7. The mean
and median of the
numbers are both 5.0. The mean is shown on the histogram as a small blue line;
the median is shown as a small purple line. The standard deviation is 1.15.
Note that the standard
deviation is calculated using N rather than N1 since the numers are considered
to be the entire populaiton of interest. A red line extends one sd in each
direction from the mean. You
can change the values of the data set by "painting" the histogram
with the mouse.
Below the histogram are shown: 

The means of these 5 quantities are displayed at the bottom of the screen.