This type of problem is a permutation problem. Permutation is the arrangement of a set with certain order. In the problem, if there are 9 members, and 3 positions are available without repeating, we can write the expression as 9P3 - 3 non repeating positions in a set of 9 elements. By evaluating, we will have 9! / (9-3)! = 504. The answer is 504.
