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A palindrome is a number that reads the same forward and backward. How many 5-digit palindromes are divisible by 9?
For ( 5a4 ) divisible by 9: sum of digits must be multiple of 9. Digits: ( 5 + a + 4 = 9 + a ) must be divisible by 9 → ( 9+a = 9 ) or ( 18 ). So ( a = 0 ) or ( a = 9 ). Mathcounts National Sprint Round Problems And Solutions
So we must be careful: The complement (not multiple of 8) requires product ≠0 and < 2³ twos. A palindrome is a number that reads the