A word that reads the same from left to right and right to left is a palindrome

Question

A word that reads the same from left to right and right to left is a palindrome. For example, "I", "noon" and "racecar" are palindromes. In the following, we consider palindromic integers. Note that the first digit of an integer cannot be 0.

A word that reads the same from left to right and right to left is a palindrome. For example, "I", "noon" and "racecar" are palindromes. In the following, we consider palindromic integers. Note that the first digit of an integer cannot be 0. How many positive palindromic integers are . 5-digit long, 900 900 5-digit long and even 400 400 5-digit long and contain 7 or 8? 58 58

Explanation / Answer

"5-digit long" positive palindromic integers are : 9*10*10 = 900

"5-digit long and even" positive palindromic integers are : 4*10*10 = 400

"5-digit long and contain 7 or 8 (not both)" positive palindromic integers are : 2*9*9 = 162

"5-digit long and contain 7 or 8 (both)" positive palindromic integers are : 2*10*10 = 200

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