The first and last, and the second and third.
9999
A 9-digit palindrome has the structure where the first five digits determine the last four digits in reverse order. The first digit must be from 1 to 9 (to ensure it's a 9-digit number), giving us 9 options. The next four digits (the second to fifth digits) can each be any digit from 0 to 9, providing 10 options each. Therefore, the total number of 9-digit palindromes is (9 \times 10^4 = 90,000).
5335
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 .
9,999,876 is the greatest seven-digit number using four different digits.
9999
A 9-digit palindrome has the structure where the first five digits determine the last four digits in reverse order. The first digit must be from 1 to 9 (to ensure it's a 9-digit number), giving us 9 options. The next four digits (the second to fifth digits) can each be any digit from 0 to 9, providing 10 options each. Therefore, the total number of 9-digit palindromes is (9 \times 10^4 = 90,000).
5335
9347 is not a digit but four digits.
If you realize that a 4 digit palindrome is basically a two digit number followed by it's own reverse, you can re-phrase this question as 'how many two digit numbers are there?' Which would then mean that (if you're considering zeros as digits without a non-zero leading term) there would be a 4 digit palindrome 0000 for the two digit 00; a four digit 0110 for the two digit 01; 0220, 02; etc etc. So the number of four digit palindromes would be the same as the quantity of whole numbers from 00 to 99. So I believe the total answer to your question would be 100.
1221
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 .
the answer is ofcourse 9999. If you insist that the first and second digit be different then it would be 9889.
9,999,876 is the greatest seven-digit number using four different digits.
9876 is the largest four digit number you can make if all the digits must be different.
The greatest 4-digit number with no repeated digits is... 9876
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.