The tns file allows students to explore in what ways changes to data affects either the mean or median or both. For example, if one value is changed slightly then the median usually will not change, but the mean will.
In problems 1 to 5 small data sets are displayed in a spreadsheet and two dot plots are drawn, one with a vertical line indicating the median and one indicating the mean. But which is which? Students are able to drag individual points left or right and see the resulting changes to the data and the two averages. In problem 6 students are able to enter their own data set.
The interactivity allows students to gain a better understanding of what these averages are and how changes in the values can affect them.
A lesson using this activity is described by Allan Duncan in a booklet entitled Inspired Connections in Maths Lessons. This description makes clear the power of the dynamically linked dual representations of data to enhance student understanding. For a pdf version of the entire booklet please click here.