An investor has two stocks: stock Y and stock Z. Each stock may increase in value, decrease in value, or remain unchanged. Consider the experiment of investing in the two stocks and observing the change (if any) in value.

a. Construct a tree diagram for this experiment.

b. Use the tree diagram to construct the sample space for this experiment.

c. If possible, calculate the probability that at least one of the stocks will increase in value.

If not possible, clearly explain why not.