Question 35897: 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, -27), (1, -27), (2, -4), (3, 1020)}. In the displayed order of S, the nonnegative probability weights are [1/(28), 23/(28), 4/(28), 0/(28)], 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, -27), (1, -27), (2, -4), (3, 1020)}. In the displayed order of S, the nonnegative probability weights are [1/(28), 23/(28), 4/(28), 0/(28)], 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, 23, 4, 0)

Variance ORIGINAL nonnegative RAW weights sum = 28

source roles = [[0, 1, 2, 3], powerset(S), [-27, -27, -4, 1020], [1, 23, 4, 0], 28, null, null]

derived = [Yes]

Variance weight times transformed value i=0 := mul(1, -27)

Variance weight times transformed value i=0 = -27

source roles = [0, 0, -27, 1, null, null]

derived = [-27, 1/28]

Variance weight times transformed value i=1 := mul(23, -27)

Variance weight times transformed value i=1 = -621

source roles = [1, 1, -27, 23, null, null]

derived = [-27, 23/28]

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, 1/7]

Variance weight times transformed value i=3 := mul(0, 1020)

Variance weight times transformed value i=3 = 0

source roles = [3, 3, 1020, 0, null, null]

derived = [1020, 0]

Variance mean numerator sum wY := sum(-27, -621, -16, 0)

Variance mean numerator sum wY = -664

Variance exact expectation M over q := div(-664, 28)

Variance exact expectation M over q = -166/7

Variance i=0 Y times q := mul(-27, 28)

Variance i=0 Y times q = -756

Variance i=0 centered integer numerator := sub(-756, -664)

Variance i=0 centered integer numerator = -92

Variance i=0 centered numerator squared := mul(-92, -92)

Variance i=0 centered numerator squared = 8464

Variance i=0 weight times squared numerator := mul(1, 8464)

Variance i=0 weight times squared numerator = 8464

Variance i=1 Y times q := mul(-27, 28)

Variance i=1 Y times q = -756

Variance i=1 centered integer numerator := sub(-756, -664)

Variance i=1 centered integer numerator = -92

Variance i=1 centered numerator squared := mul(-92, -92)

Variance i=1 centered numerator squared = 8464

Variance i=1 weight times squared numerator := mul(23, 8464)

Variance i=1 weight times squared numerator = 194672

Variance i=2 Y times q := mul(-4, 28)

Variance i=2 Y times q = -112

Variance i=2 centered integer numerator := sub(-112, -664)

Variance i=2 centered integer numerator = 552

Variance i=2 centered numerator squared := mul(552, 552)

Variance i=2 centered numerator squared = 304704

Variance i=2 weight times squared numerator := mul(4, 304704)

Variance i=2 weight times squared numerator = 1218816

Variance i=3 Y times q := mul(1020, 28)

Variance i=3 Y times q = 28560

Variance i=3 centered integer numerator := sub(28560, -664)

Variance i=3 centered integer numerator = 29224

Variance i=3 centered numerator squared := mul(29224, 29224)

Variance i=3 centered numerator squared = 854042176

Variance i=3 weight times squared numerator := mul(0, 854042176)

Variance i=3 weight times squared numerator = 0

Variance sum ALL weighted squared numerators := sum(8464, 194672, 1218816, 0)

Variance sum ALL weighted squared numerators = 1421952

Variance denominator q squared := mul(28, 28)

Variance denominator q squared = 784

Variance denominator q cubed binary second factor := mul(784, 28)

Variance denominator q cubed binary second factor = 21952

Variance probability population centered sum over q cubed := div(1421952, 21952)

Variance probability population centered sum over q cubed = 3174/49

source roles = [[-27, -27, -4, 1020], [1, 23, 4, 0], 28, -166/7, 1421952, 21952]

derived = [3174/49, [-27, -4], No]

source roles = [zero_variance, null, null]

derived = [3174/49]

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.