Use the definition of an r-permutation, or the product rule to determine the number of trifectas possible in a race with 9 horses. A trifecta is the correct ordering of the first three horses to...

Extracted text: Use the definition of an r-permutation, or the product rule to determine the number of trifectas possible in a race with 9 horses. A trifecta is the correct ordering of the first three horses to finish the race, i.e. an individual correctly picks the winner of the race, the second place finisher (place), and the third place finisher (show). The result may be left in product notation, i.e. aj · Az ·…·.