An important point in this example is that reasoning and proof enabled students to abstract and codify their observations. Chuen's initial observation was that if each of two numbers is multiplied by 10.9, the mean of the resulting numbers is 10.9 times the mean of the original numbers. The reasoning he used ultimately produced the argument that if every number in a data set is multiplied by a constant, the mean of the resulting data set equals the mean of the original data set multiplied by that constant. The fact that this argument could be made algebraically furnished a mechanism for making a similar argument about the standard deviation. In this way, results with similar justifications can emerge.