For each of the last four digits, there are nine possible digits to choose from (since we cannot use 8). So the number of possible telephone numbers would be

9 x 9 x 9 x 9 = 6,561.

900. There are 9 possible choices for the 1st/5th digit (because you can't use zero), 10 possible choices for the 2nd/4th digit, and 10 possible choices for the 3rd digit. So 9 x 10 x 10 = 900.4. A number that is a palindrome reads the same forward and backward. 90 three-digit plaindormes adn 90 four-digit palindromes exist. How many five-digit palindromes exist?

01