Question 35889: 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, -19), (1, -19), (2, -4), (3, 1012)}. In the displayed order of S, the nonnegative probability weights are [1/(20), 15/(20), 4/(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, -19), (1, -19), (2, -4), (3, 1012)}. In the displayed order of S, the nonnegative probability weights are [1/(20), 15/(20), 4/(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, 15, 4, 0)

Variance ORIGINAL nonnegative RAW weights sum = 20

source roles = [[0, 1, 2, 3], powerset(S), [-19, -19, -4, 1012], [1, 15, 4, 0], 20, null, null]

derived = [Yes]

Variance weight times transformed value i=0 := mul(1, -19)

Variance weight times transformed value i=0 = -19

source roles = [0, 0, -19, 1, null, null]

derived = [-19, 1/20]

Variance weight times transformed value i=1 := mul(15, -19)

Variance weight times transformed value i=1 = -285

source roles = [1, 1, -19, 15, null, null]

derived = [-19, 3/4]

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

Variance weight times transformed value i=2 = -16

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

derived = [-4, 1/5]

Variance weight times transformed value i=3 := mul(0, 1012)

Variance weight times transformed value i=3 = 0

source roles = [3, 3, 1012, 0, null, null]

derived = [1012, 0]

Variance mean numerator sum wY := sum(-19, -285, -16, 0)

Variance mean numerator sum wY = -320

Variance exact expectation M over q := div(-320, 20)

Variance exact expectation M over q = -16

Variance i=0 Y times q := mul(-19, 20)

Variance i=0 Y times q = -380

Variance i=0 centered integer numerator := sub(-380, -320)

Variance i=0 centered integer numerator = -60

Variance i=0 centered numerator squared := mul(-60, -60)

Variance i=0 centered numerator squared = 3600

Variance i=0 weight times squared numerator := mul(1, 3600)

Variance i=0 weight times squared numerator = 3600

Variance i=1 Y times q := mul(-19, 20)

Variance i=1 Y times q = -380

Variance i=1 centered integer numerator := sub(-380, -320)

Variance i=1 centered integer numerator = -60

Variance i=1 centered numerator squared := mul(-60, -60)

Variance i=1 centered numerator squared = 3600

Variance i=1 weight times squared numerator := mul(15, 3600)

Variance i=1 weight times squared numerator = 54000

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

Variance i=2 Y times q = -80

Variance i=2 centered integer numerator := sub(-80, -320)

Variance i=2 centered integer numerator = 240

Variance i=2 centered numerator squared := mul(240, 240)

Variance i=2 centered numerator squared = 57600

Variance i=2 weight times squared numerator := mul(4, 57600)

Variance i=2 weight times squared numerator = 230400

Variance i=3 Y times q := mul(1012, 20)

Variance i=3 Y times q = 20240

Variance i=3 centered integer numerator := sub(20240, -320)

Variance i=3 centered integer numerator = 20560

Variance i=3 centered numerator squared := mul(20560, 20560)

Variance i=3 centered numerator squared = 422713600

Variance i=3 weight times squared numerator := mul(0, 422713600)

Variance i=3 weight times squared numerator = 0

Variance sum ALL weighted squared numerators := sum(3600, 54000, 230400, 0)

Variance sum ALL weighted squared numerators = 288000

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(288000, 8000)

Variance probability population centered sum over q cubed = 36

source roles = [[-19, -19, -4, 1012], [1, 15, 4, 0], 20, -16, 288000, 8000]

derived = [36, [-19, -4], No]

source roles = [zero_variance, null, null]

derived = [36]

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.