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Q: What is the sum of all 4 digit numbers that are the same when their digits are reversed?

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The same as the number of two-digit numbers, since the last two digits must the same as the first two, only reversed. So I'll say there are 100 four-digit palindromes.

The same as the number of two-digit numbers, since the last two digits must the same as the first two, only reversed. So I'll say there are 100 four-digit palindromes.

An eight digit number with one zero cannot remain the same when its digits are reversed. It must have an even number of 0s.

987654

2

There are 900 of them.

It is 987654321.

Any pair of digits (not including 0), can be used to generate 14 four-digit numbers. If one of the digits is 0, only seven will start with a non-zero digit.

Exactly 2: 243 of them.

1

The number of six digit numbers that you can make from ten different digits ifrepetitions of same digit on the six digit number is allowed is 1 000 000 numbers(including number 000 000).If no repetitions of the the same digit are allowed then you have:10P6 = 10!/(10-6)! = 151 200 different six digit numbers(six digit permutations form 10 different digits).

The same way you kfind it for 2 & 1 digits. :)

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