Probability that a 4-digit number is a palindrome?

Probability that a 4-digit number is a palindrome?

Approach: Count palindromes (ABBA) / total 4-digit numbers.

1/100. 9 choices for A, 10 for B. 90 / 9000 = 1/100.

Follow-up: How many 5-digit palindromes are there?

Key concepts: counting.