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How many $7$ digit palindromes can be formed using the digits $2,2,3,3,5,5,5?$

 Oct 27, 2019
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We can write this number as abcdcba. We know that d must be 5 since there are an odd number of fives. We now have 3 choices left for a,b, and c. Each of the permutations of those 3 choices will end up in 6 different palindromes that can be formed.

 Oct 27, 2019

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