Question: how to calculate the number of combinations in a lock?
Answer: Answer: There are 9,999 different combinations in a 4-digit lock. Explanation: The 4-digit number on a lock begins from 0000 and ends up to 9999 which are: From 0000 to 0999 there are 999 combinations. ( ...  From 1,000 to 9,999 there are 8,999 combinations (9,000) And now we have 1,000+9,000=10,000 combinations total.