The numbers 0 through 9 are used in code groups of two to identify an item of clothing. Code 83 might identify a blue blouse, size medium. The code group 46 might identify a pair of pants, size 18, and so on. Repetitions of numbers are not permitted, i.e., the same number cannot be used more than once in a total sequence. As examples, 27, 94 or 55 would not be permitted. How many different code groups can be designed?