A bag contains 9 tiles, each with a different number from 1 - 9. You chose a tile without looking, put it aside, choose a second tile without looking, put it aside, then choose a third tile without looking. What is the probability that you choose tiles with the numbers 1, 2, and 3 in that order?

Someone pls explain this. I know the answer is 1/504 but how do you get there?