Keep the d8 or gamble on the d12?

You roll a fair 88-sided die once. You may keep its value, or discard it and instead roll a fair 1212-sided die once, taking that value. Under optimal play, what is your expected payout?

Show hints (2)+
  1. The reroll is worth E[d12]=6.5\mathbb{E}[d_{12}]=6.5. Keep the d8d_8 only when it exceeds that.
  2. Keep {7,8}\{7,8\}, else take 6.56.5: 6⋅6.5+7+88\tfrac{6\cdot6.5+7+8}{8}.

Answer

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6.75 (± 0.01)

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