Okay, so this program will generate two postal codes.

After it generates the first one, the second one has to be the exact same one. (Regardless of what the first one was.)

There is only one postal code that is exactly the same, hence the probability is 1/17,576,000

2/17,576,000 would be the chance that the machine generates one of 2 pre-specified postal codes.

Hope this helps.