If the two must be different digits, then there 20 possibilities.
If they can be the same one, then there are 25 possibilities.
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17
It would help to know which digit. 0 appears in 9 numbers and each of the others in 18 numbers.
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Without repeats there are 4 × 3 = 12 possible 2 digit numbers. With repeats there are 4 × 4 = 16 possible 2 digit numbers.