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Loaded dice with an evenly spread total

Question

Two six-sided dice, faces numbered 1 to 6, may each be loaded in any way you like (independently). Can they be weighted so that every total from 2 to 12 is equally likely?

Short answer

No. Uniform totals force p1q1=p6q6=111p_1q_1=p_6q_6=\tfrac1{11}. But a total of 7 includes the outcomes (1,6)(1,6) and (6,1)(6,1), so 111≥p1q6+p6q1=111(p1p6+p6p1)\tfrac1{11}\ge p_1q_6+p_6q_1=\tfrac1{11}\left(\tfrac{p_1}{p_6}+\tfrac{p_6}{p_1}\right), requiring x+1x≤1x+\tfrac1x\le1 for some x>0x>0, which is impossible since x+1x≥2x+\tfrac1x\ge2.

Adapted from OpenQuant; question and answer rewritten by SelfMadeQuant.com.

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