Brute Force - Part One

 Assuming I can guess two incorrect PINs every three hours before the ATM swallows my card,   ((2 PINs)/(3 Hours))*(24 Hours) gives me 16 PINs per day.  The average time to crack my PIN would be ((10000 Possible PINs)/2)*(1 Day)/(16 PINs) would be 312.5 days.

The worst case senario, assuming the last combination I try (9999) is the correct one gives: ((10000 Possible PINs)/2)*(1 Day)/(16 PINs) or 625 days.