The state of Utah appends a ninth digit a9 to an eight-digit driver’s license number a1a2 . . . a8 so that (9a1 + 8a2 + 7a3 + 6a4 + 5a5 + 4a6 + 3a7 + 2a8 + a9) mod 10 = 0. If you know that the license number 149105267 has exactly one digit incorrect, explain why the error cannot be in position 2, 4, 6, or 8.
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