An odd subset with two small elements

How many subsets of {1,2,,10}\{1, 2, \dots, 10\} contain exactly two elements from {1,2,3}\{1, 2, 3\} and consist of only odd numbers?

Show hints (2)+
  1. "Only odd" means eligible elements are {1,3,5,7,9}\{1,3,5,7,9\}. The odd members of {1,2,3}\{1,2,3\} are just {1,3}\{1,3\}.
  2. Exactly two from {1,2,3}\{1,2,3\} forces {1,3}\{1,3\}; the rest is any subset of {5,7,9}\{5,7,9\} (232^3).

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Asked at: Jane Street, Citadel

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