Which side holds the heavy weight

Six weights of masses 201,202,…,206201, 202, \dots, 206 grams are split at random, three to each pan of a balance. What is the probability that the pan containing the 206206-gram weight is the heavier pan?

Show hints (2)+
  1. The 206206-pan is heavier iff its total exceeds half of 12211221, i.e. its two companions sum to ≥405\ge 405.
  2. Count the (52)=10\binom{5}{2}=10 companion-pairs; only {201,202}\{201,202\} and {201,203}\{201,203\} fall short.

Answer

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