Sam has nine flower pots, and want to display four of them on the front porch in a row, and the other five in a second row. (The order of the pots matters.) How many different displays are possible?

Choose any 4 of the 9 to be on the first row and arrange them in 4! = 24 ways

The other 5 are assigned to the second row automatically and can be arranged in 5! =120 ways

So....the number of possible displays = C(9,4) * 4! * 5! = 362880