Sum of repeating decimals

Compute the sum of all numbers of the form 0.abc0.\overline{abc} (i.e. 0.abcabcabc0.abcabcabc\dots) where a,b,ca, b, c are distinct digits from 00 to 99.

Show hints (2)+
  1. 0.abc=(100a+10b+c)/9990.\overline{abc}=(100a+10b+c)/999. Sum over the 109810\cdot9\cdot8 distinct-digit triples.
  2. By symmetry each position sums to 7245=324072\cdot45=3240; total =1113240/999=111\cdot3240/999.

Answer

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360

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Asked at: Jane Street, Two Sigma

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