What is the smallest four-digit number that reads identically forwards and backwards and is also an exact multiple of 9?
1881
A four-digit palindrome has the format ABBA, and for it to be divisible by 9, the sum of its digits (2A + 2B) must be a multiple of 9, meaning A + B must equal 9. To minimize the four-digit number, choose the smallest valid leading digit A = 1, forcing B = 8, yielding 1881.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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