For the first digit we have 9 options (cannot start with zero).
For the second and third digits we can accept any number between 0 and 9 (ie we have 10 options).
For the fourth and fifth digits, there is only one option, as they must be equal to the second and first digits, respectively.
ABCBA = 9 x 10 x 10 x 1 x 1 = 900
There are 900 5-digit palindrome numbers!
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