probability of repeated numberplate

Firstly, I'm not sure this is the right forum, but it's harder than anything I did in high school so I'm putting it here, mods feel free to move it

I don't think it's a hard question, I'm just very rusty with my probability

For a Traffic engineering subject I've conducted traffic counts for a section of road, recording the digits from the number plate (Victorian (AUS) Plates, format ABC 123).

If I've got 'n' results, what's the probability of having a repeated numberplate.