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jmc

number theory junior

Problem

How many 4-digit numbers greater than 1000 are there that use the four digits of 2012?
(A)
(B)
(C)
(D)
Solution
For this problem, all we need to do is find the amount of valid 4-digit numbers that can be made from the digits of , since all of the valid 4-digit number will always be greater than . The best way to solve this problem is by using casework. There can be only two leading digits, namely or . When the leading digit is , you can make such numbers. When the leading digit is , you can make such numbers. Summing the amounts of numbers, we find that there are such numbers.
Final answer
D