The first and last, and the second and third.
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9999
5335
9,999,876 is the greatest seven-digit number using four different digits.
The first digit can be any one of nine (all except zero). For each of those . . .The second digit can be any one of ten.Total possibilities for the first two digits = 9 x 10 = 90.Since the 4-digit number is a palindrome, the 3rd and 4th digits are determinedby the 1st and 2nd ones.So the total number of 4-digit palindromes is the same as the number of possibilitiesfor the first 2 digits = 90 .
9876 is the largest four digit number you can make if all the digits must be different.