Chapter 45: Representing Standard Deviation: Situation 39 From the MACMTL–CPTM Situations Project

In prior lessons, students learned to compute mean, mode, and median. The teacher presented the formula for standard deviation and had students work through an example of computing the standard deviation with data from a summer-job context. The written work in Figure 45.1 developed during the example.

The teacher then said, “Standard deviation is a measure of the consistency of our data set. Do you know what consistency means?” To explain consistency the teacher used the idea of throwing darts. One student pursued the analogy, “If you hit the bull’s eye, your standard deviation would be lower. But if you’re all over the board, your standard deviation would be higher.” The student drew the picture in Figure 45.2 to illustrate his idea: