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jmc

counting and probability junior

Problem

A palindrome is a number that reads the same forwards and backwards, such as 3003. How many positive four-digit integers are palindromes?
Solution
Constructing palindromes requires that we choose the thousands digit (which defines the units digit) and the hundreds digit (which defines the tens digit). Since there are 9 choices for the thousands digit, and 10 choices for the hundreds digit, creating palindromes.
Final answer
90