ID numbers all have 7 digits from 0 to 9. We will assume that all digits can be 0 through 9
This is a homework problem, but I am afraid I am very lost, though I think I am over thinking it.
I know this is the pigeon hole theorom in which if you have N pigeons and k pigeon holes then there is at least on hole with the ceiling of N/k pigeons.
I just don't know how to apply that idea here.
The next question is similar: How many ID numbers must you have to guarantee that at least four of them have the same last 2 digits?
Would the process for this one be different than the first one?