There is a 9 digit number which reads the same backward as forward. At most, how many unique digits will be there in this number.A3B5C6D9
Question
There is a 9 digit number which reads the same backward as forward. At most, how many unique digits will be there in this number.A3B5C6D9
Solution
The number you're referring to is a palindrome, which means it reads the same backward as forward. A 9-digit palindromic number will have the following structure: ABCDEEDCBA.
However, since it's a 9-digit number, one of the digits in the middle will not be repeated. So, the structure will look like this: ABCDEDCBA.
This means that at most, there can be 5 unique digits in this number. The first digit (A) cannot be 0, so it can be any digit from 1 to 9. The remaining 4 digits (B, C, D, E) can be any digit from 0 to 9.
So, the answer is D9.
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