Question 35887: Zero Variance on Positive-Probability Support

Original question and givens

The nonempty finite sample space is S={0, 1, 2, 3}, with event family F=𝒫(S). The total function X:S→R has table {(0, -17), (1, -17), (2, -4), (3, 1010)}. In the displayed order of S, the nonnegative probability weights are [1/(20), 13/(20), 6/(20), 0/(20)], summing exactly to one. Is Var(X)=0 under this probability law? Constancy is required only at positive-weight outcomes.

• G001 — The nonempty finite sample space is S={0, 1, 2, 3}, with event family F=𝒫(S). The total function X:S→R has table {(0, -17), (1, -17), (2, -4), (3, 1010)}. In the displayed order of S, the nonnegative probability weights are [1/(20), 13/(20), 6/(20), 0/(20)], summing exactly to one. Is Var(X)=0 under this probability law? Constancy is required only at positive-weight outcomes.

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

• mko-variance

Step-by-step derivation

source roles = [qf-variance-zero-support, [F, S, denominator, operation, values, weights]]

derived = [variance, zero_variance, null]

Variance ORIGINAL nonnegative RAW weights sum := sum(1, 13, 6, 0)

Variance ORIGINAL nonnegative RAW weights sum = 20

source roles = [[0, 1, 2, 3], powerset(S), [-17, -17, -4, 1010], [1, 13, 6, 0], 20, null, null]

derived = [Yes]

Variance weight times transformed value i=0 := mul(1, -17)

Variance weight times transformed value i=0 = -17

source roles = [0, 0, -17, 1, null, null]

derived = [-17, 1/20]

Variance weight times transformed value i=1 := mul(13, -17)

Variance weight times transformed value i=1 = -221

source roles = [1, 1, -17, 13, null, null]

derived = [-17, 13/20]

Variance weight times transformed value i=2 := mul(6, -4)

Variance weight times transformed value i=2 = -24

source roles = [2, 2, -4, 6, null, null]

derived = [-4, 3/10]

Variance weight times transformed value i=3 := mul(0, 1010)

Variance weight times transformed value i=3 = 0

source roles = [3, 3, 1010, 0, null, null]

derived = [1010, 0]

Variance mean numerator sum wY := sum(-17, -221, -24, 0)

Variance mean numerator sum wY = -262

Variance exact expectation M over q := div(-262, 20)

Variance exact expectation M over q = -131/10

Variance i=0 Y times q := mul(-17, 20)

Variance i=0 Y times q = -340

Variance i=0 centered integer numerator := sub(-340, -262)

Variance i=0 centered integer numerator = -78

Variance i=0 centered numerator squared := mul(-78, -78)

Variance i=0 centered numerator squared = 6084

Variance i=0 weight times squared numerator := mul(1, 6084)

Variance i=0 weight times squared numerator = 6084

Variance i=1 Y times q := mul(-17, 20)

Variance i=1 Y times q = -340

Variance i=1 centered integer numerator := sub(-340, -262)

Variance i=1 centered integer numerator = -78

Variance i=1 centered numerator squared := mul(-78, -78)

Variance i=1 centered numerator squared = 6084

Variance i=1 weight times squared numerator := mul(13, 6084)

Variance i=1 weight times squared numerator = 79092

Variance i=2 Y times q := mul(-4, 20)

Variance i=2 Y times q = -80

Variance i=2 centered integer numerator := sub(-80, -262)

Variance i=2 centered integer numerator = 182

Variance i=2 centered numerator squared := mul(182, 182)

Variance i=2 centered numerator squared = 33124

Variance i=2 weight times squared numerator := mul(6, 33124)

Variance i=2 weight times squared numerator = 198744

Variance i=3 Y times q := mul(1010, 20)

Variance i=3 Y times q = 20200

Variance i=3 centered integer numerator := sub(20200, -262)

Variance i=3 centered integer numerator = 20462

Variance i=3 centered numerator squared := mul(20462, 20462)

Variance i=3 centered numerator squared = 418693444

Variance i=3 weight times squared numerator := mul(0, 418693444)

Variance i=3 weight times squared numerator = 0

Variance sum ALL weighted squared numerators := sum(6084, 79092, 198744, 0)

Variance sum ALL weighted squared numerators = 283920

Variance denominator q squared := mul(20, 20)

Variance denominator q squared = 400

Variance denominator q cubed binary second factor := mul(400, 20)

Variance denominator q cubed binary second factor = 8000

Variance probability population centered sum over q cubed := div(283920, 8000)

Variance probability population centered sum over q cubed = 3549/100

source roles = [[-17, -17, -4, 1010], [1, 13, 6, 0], 20, -131/10, 283920, 8000]

derived = [3549/100, [-17, -4], No]

source roles = [zero_variance, null, null]

derived = [3549/100]

Reverse checks

• S035 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S034 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S033 · premise_and_result_audit — Recompute Variance probability population centered sum over q cubed with exact rational arithmetic, not rounded decimals.
• S032 · premise_and_result_audit — Recompute Variance denominator q cubed binary second factor with exact rational arithmetic, not rounded decimals.
• S031 · premise_and_result_audit — Recompute Variance denominator q squared with exact rational arithmetic, not rounded decimals.
• S030 · premise_and_result_audit — Recompute Variance sum ALL weighted squared numerators with exact rational arithmetic, not rounded decimals.
• S029 · premise_and_result_audit — Recompute Variance i=3 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S028 · premise_and_result_audit — Recompute Variance i=3 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S027 · premise_and_result_audit — Recompute Variance i=3 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S026 · premise_and_result_audit — Recompute Variance i=3 Y times q with exact rational arithmetic, not rounded decimals.
• S025 · premise_and_result_audit — Recompute Variance i=2 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S024 · premise_and_result_audit — Recompute Variance i=2 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S023 · premise_and_result_audit — Recompute Variance i=2 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S022 · premise_and_result_audit — Recompute Variance i=2 Y times q with exact rational arithmetic, not rounded decimals.
• S021 · premise_and_result_audit — Recompute Variance i=1 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S020 · premise_and_result_audit — Recompute Variance i=1 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S019 · premise_and_result_audit — Recompute Variance i=1 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S018 · premise_and_result_audit — Recompute Variance i=1 Y times q with exact rational arithmetic, not rounded decimals.
• S017 · premise_and_result_audit — Recompute Variance i=0 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S016 · premise_and_result_audit — Recompute Variance i=0 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S015 · premise_and_result_audit — Recompute Variance i=0 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S014 · premise_and_result_audit — Recompute Variance i=0 Y times q with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute Variance exact expectation M over q with exact rational arithmetic, not rounded decimals.
• S012 · premise_and_result_audit — Recompute Variance mean numerator sum wY with exact rational arithmetic, not rounded decimals.
• S011 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S010 · premise_and_result_audit — Recompute Variance weight times transformed value i=3 with exact rational arithmetic, not rounded decimals.
• S009 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S008 · premise_and_result_audit — Recompute Variance weight times transformed value i=2 with exact rational arithmetic, not rounded decimals.
• S007 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S006 · premise_and_result_audit — Recompute Variance weight times transformed value i=1 with exact rational arithmetic, not rounded decimals.
• S005 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S004 · premise_and_result_audit — Recompute Variance weight times transformed value i=0 with exact rational arithmetic, not rounded decimals.
• S003 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.
• S002 · premise_and_result_audit — Recompute Variance ORIGINAL nonnegative RAW weights sum with exact rational arithmetic, not rounded decimals.
• S001 · premise_and_result_audit — Reverse-audit THIS question’s original operands,roles and necessary premises;reconstruct the next step,without reversing a one-way implication.Numerical/finite-table checking is not formal proof of an arbitrary theorem.Original Q,bilingual sources,MKO,AST,status and history remain preserved.

Result

No

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.