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The GMAT math problem takes two numbers from 1, 2 and 3 ... to 9 to form a three-digit number (where the two numbers are the same). How many ways are there?
First, choose two out of nine numbers, C.
Two numbers form three digits, one of which is repeated first, and then the other has three "spaces", which can be inserted at will.
Then C.
So there are 36*6=2 16 digits that meet the requirements.