Question 35818: Probability Variance after Scaling

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, -23), (1, -23), (2, -4), (3, 1016)}. In the displayed order of S, the nonnegative probability weights are [1/(24), 19/(24), 4/(24), 0/(24)], summing exactly to one. Put Z=(-3)X. Find Var(Z)=E[(Z−E[Z])²] exactly as a reduced positive-denominator fraction. This is probability-distribution variance, not sample variance with an n−1 denominator.

• 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, -23), (1, -23), (2, -4), (3, 1016)}. In the displayed order of S, the nonnegative probability weights are [1/(24), 19/(24), 4/(24), 0/(24)], summing exactly to one. Put Z=(-3)X. Find Var(Z)=E[(Z−E[Z])²] exactly as a reduced positive-denominator fraction. This is probability-distribution variance, not sample variance with an n−1 denominator.

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-scale, [F, S, denominator, k, operation, values, weights]]

derived = [variance, scale_variance, null]

Variance ORIGINAL nonnegative RAW weights sum := sum(1, 19, 4, 0)

Variance ORIGINAL nonnegative RAW weights sum = 24

source roles = [[0, 1, 2, 3], powerset(S), [-23, -23, -4, 1016], [1, 19, 4, 0], 24, -3, null]

derived = [Yes]

Variance transformed ORIGINAL value i=0 := mul(-3, -23)

Variance transformed ORIGINAL value i=0 = 69

Variance weight times transformed value i=0 := mul(1, 69)

Variance weight times transformed value i=0 = 69

source roles = [0, 0, -23, 1, -3, null]

derived = [69, 1/24]

Variance transformed ORIGINAL value i=1 := mul(-3, -23)

Variance transformed ORIGINAL value i=1 = 69

Variance weight times transformed value i=1 := mul(19, 69)

Variance weight times transformed value i=1 = 1311

source roles = [1, 1, -23, 19, -3, null]

derived = [69, 19/24]

Variance transformed ORIGINAL value i=2 := mul(-3, -4)

Variance transformed ORIGINAL value i=2 = 12

Variance weight times transformed value i=2 := mul(4, 12)

Variance weight times transformed value i=2 = 48

source roles = [2, 2, -4, 4, -3, null]

derived = [12, 1/6]

Variance transformed ORIGINAL value i=3 := mul(-3, 1016)

Variance transformed ORIGINAL value i=3 = -3048

Variance weight times transformed value i=3 := mul(0, -3048)

Variance weight times transformed value i=3 = 0

source roles = [3, 3, 1016, 0, -3, null]

derived = [-3048, 0]

Variance mean numerator sum wY := sum(69, 1311, 48, 0)

Variance mean numerator sum wY = 1428

Variance exact expectation M over q := div(1428, 24)

Variance exact expectation M over q = 119/2

Variance i=0 Y times q := mul(69, 24)

Variance i=0 Y times q = 1656

Variance i=0 centered integer numerator := sub(1656, 1428)

Variance i=0 centered integer numerator = 228

Variance i=0 centered numerator squared := mul(228, 228)

Variance i=0 centered numerator squared = 51984

Variance i=0 weight times squared numerator := mul(1, 51984)

Variance i=0 weight times squared numerator = 51984

Variance i=1 Y times q := mul(69, 24)

Variance i=1 Y times q = 1656

Variance i=1 centered integer numerator := sub(1656, 1428)

Variance i=1 centered integer numerator = 228

Variance i=1 centered numerator squared := mul(228, 228)

Variance i=1 centered numerator squared = 51984

Variance i=1 weight times squared numerator := mul(19, 51984)

Variance i=1 weight times squared numerator = 987696

Variance i=2 Y times q := mul(12, 24)

Variance i=2 Y times q = 288

Variance i=2 centered integer numerator := sub(288, 1428)

Variance i=2 centered integer numerator = -1140

Variance i=2 centered numerator squared := mul(-1140, -1140)

Variance i=2 centered numerator squared = 1299600

Variance i=2 weight times squared numerator := mul(4, 1299600)

Variance i=2 weight times squared numerator = 5198400

Variance i=3 Y times q := mul(-3048, 24)

Variance i=3 Y times q = -73152

Variance i=3 centered integer numerator := sub(-73152, 1428)

Variance i=3 centered integer numerator = -74580

Variance i=3 centered numerator squared := mul(-74580, -74580)

Variance i=3 centered numerator squared = 5562176400

Variance i=3 weight times squared numerator := mul(0, 5562176400)

Variance i=3 weight times squared numerator = 0

Variance sum ALL weighted squared numerators := sum(51984, 987696, 5198400, 0)

Variance sum ALL weighted squared numerators = 6238080

Variance denominator q squared := mul(24, 24)

Variance denominator q squared = 576

Variance denominator q cubed binary second factor := mul(576, 24)

Variance denominator q cubed binary second factor = 13824

Variance probability population centered sum over q cubed := div(6238080, 13824)

Variance probability population centered sum over q cubed = 1805/4

source roles = [[69, 69, 12, -3048], [1, 19, 4, 0], 24, 119/2, 6238080, 13824]

derived = [1805/4, [12, 69], No]

source roles = [scale_variance, -3, null]

derived = [1805/4]

Reverse checks

• S039 · 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.
• S038 · 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.
• S037 · premise_and_result_audit — Recompute Variance probability population centered sum over q cubed with exact rational arithmetic, not rounded decimals.
• S036 · premise_and_result_audit — Recompute Variance denominator q cubed binary second factor with exact rational arithmetic, not rounded decimals.
• S035 · premise_and_result_audit — Recompute Variance denominator q squared with exact rational arithmetic, not rounded decimals.
• S034 · premise_and_result_audit — Recompute Variance sum ALL weighted squared numerators with exact rational arithmetic, not rounded decimals.
• S033 · premise_and_result_audit — Recompute Variance i=3 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S032 · premise_and_result_audit — Recompute Variance i=3 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S031 · premise_and_result_audit — Recompute Variance i=3 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S030 · premise_and_result_audit — Recompute Variance i=3 Y times q with exact rational arithmetic, not rounded decimals.
• S029 · premise_and_result_audit — Recompute Variance i=2 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S028 · premise_and_result_audit — Recompute Variance i=2 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S027 · premise_and_result_audit — Recompute Variance i=2 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S026 · premise_and_result_audit — Recompute Variance i=2 Y times q with exact rational arithmetic, not rounded decimals.
• S025 · premise_and_result_audit — Recompute Variance i=1 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S024 · premise_and_result_audit — Recompute Variance i=1 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S023 · premise_and_result_audit — Recompute Variance i=1 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S022 · premise_and_result_audit — Recompute Variance i=1 Y times q with exact rational arithmetic, not rounded decimals.
• S021 · premise_and_result_audit — Recompute Variance i=0 weight times squared numerator with exact rational arithmetic, not rounded decimals.
• S020 · premise_and_result_audit — Recompute Variance i=0 centered numerator squared with exact rational arithmetic, not rounded decimals.
• S019 · premise_and_result_audit — Recompute Variance i=0 centered integer numerator with exact rational arithmetic, not rounded decimals.
• S018 · premise_and_result_audit — Recompute Variance i=0 Y times q with exact rational arithmetic, not rounded decimals.
• S017 · premise_and_result_audit — Recompute Variance exact expectation M over q with exact rational arithmetic, not rounded decimals.
• S016 · premise_and_result_audit — Recompute Variance mean numerator sum wY with exact rational arithmetic, not rounded decimals.
• S015 · 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.
• S014 · premise_and_result_audit — Recompute Variance weight times transformed value i=3 with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute Variance transformed ORIGINAL value i=3 with exact rational arithmetic, not rounded decimals.
• S012 · 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.
• S011 · premise_and_result_audit — Recompute Variance weight times transformed value i=2 with exact rational arithmetic, not rounded decimals.
• S010 · premise_and_result_audit — Recompute Variance transformed ORIGINAL value i=2 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=1 with exact rational arithmetic, not rounded decimals.
• S007 · premise_and_result_audit — Recompute Variance transformed ORIGINAL value i=1 with exact rational arithmetic, not rounded decimals.
• S006 · 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.
• S005 · premise_and_result_audit — Recompute Variance weight times transformed value i=0 with exact rational arithmetic, not rounded decimals.
• S004 · premise_and_result_audit — Recompute Variance transformed ORIGINAL 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

1805/4

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.