Question about number locks

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My dad has an attache case (is that how it's spelled?) whose three-number combination he has forgotten. I'm trying to open it but I'm not good enough at math to figure out how many possible combinations a three-number lock has. I tried starting from 0-0-0 and went up progressively up with 0-0-1, 0-0-2... 0-0-9, 0-1-0... 0-9-9, 1-0-0... 9-9-9 so I've essentially done 1,000 combinations. It still won't open. Is it possible the lock is just busted or is it just that I missed the right combination from my initial run-through? I really don't want to try that 1,000 tries again if I can help it. Do any of you have an idea?