10.3. For all fires in Chicago last year, data arc available on A = number of firefighters at the fire and y = cost of damages due to the fire. The correlation is positive.

(a) Does this mean that having more firefighters at a fire causes the damage to be worse?

Explain.

(b) Identify a third variable that could be a common cause of X and Y. Construct a hypothetical scattcrplot (like Figure 10.1), identifying points according to their value on the third variable, to illustrate your argument.