Final answer:
The correct option is B). The advantage of the scatter plot method is that it allows for visual inspection of the relationship between size and cost, aiding the determination of an appropriate model.
Step-by-step explanation:
One advantage of the scatter plot method for separating a mixed cost into its fixed and variable components is b. It allows a cost analyst to inspect the data visually. This visual inspection can provide a preliminary assessment of the relationship between the independent variable (size) and the dependent variable (cost), and can help in determining whether a linear relationship exists or if a different model would be more appropriate. While calculating the least-squares line and finding the correlation coefficient provide additional statistical measures, it is the scatter plot that offers an immediate and intuitive understanding of the data's behavior.
It's important to note that even if the correlation coefficient is significant, one must assess the pattern of the scatter plot and not rely solely on quantitative measures. In some cases, a non-linear model might better capture the underlying relationship between variables. As an example, if the scatter plot reveals a curved pattern, this indicates that using a line might not provide the best fit, and other methods to model the cost data should be explored.