Question: how many possible combinations on a safe?
Answer: Could it be 10C3? The safe combination could be 433 or 334; the combinations are the same, but their ordering is different. Order is important for the safe combinations, this is a permutation problem. A safe code can be made of any of the numbers {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.