Problem Analysis #36

8.32s
2,953 toks
Problem Statement

A discrete random variable XX takes integer values from 00 to 44, and its probability mass function is given byP(X=x)={2x112(x=0,1,2,3),a(x=4),\text{P}(X = x) = \begin{cases}\dfrac{|2x - 1|}{12} & (x = 0, 1, 2, 3), \\[4pt]a & (x = 4),\end{cases}where aa is a nonzero constant. ComputeV(1aX).\text{V}\left(\dfrac{1}{a}X\right).[3 points]\

Ground Truth
45
Execution Trace
Reasoning Process

[THOUGHT] We need to find the constant a using the total probability = 1, then compute Var((1/a)X) = (1/a^2) Var(X). We'll compute pmf values, check they sum to 1, solve for a, then compute E[X], E[X^2], Var(X), and finally Var((1/a)X) with Python. [/THOUGHT] [PYTHON] from fractions import Fraction

Compute probabilities for x = 0,1,2,3

probs = {x: abs(2*x - 1)/12 for x in range(4)} print("Probs x=0..3:", probs, "Sum:", sum(probs.values()))

Solve for a from total probability = 1

sum_0_3 = sum(probs.values()) a = 1 - sum_0_3 print("a =", a)

Double-check a is nonzero

assert a != 0

Define full pmf including x=4

probs[4] = a print("Full pmf:", probs, "Total sum:", sum(probs.values()))

Compute E[X] and E[X^2]

EX = sum(x * p for x, p in probs.items()) EX2 = sum((x2) * p for x, p in probs.items()) VarX = EX2 - EX2 print("E[X] =", EX) print("E[X^2] =", EX2) print("Var(X) =", VarX)

Compute Var((1/a)X) = (1/a^2) Var(X)

Var_scaled = VarX / (a**2) print("Var((1/a) X) =", Var_scaled) [/PYTHON]

Tool Output
[PYTHON OUTPUT] Probs x=0..3: {0: 0.08333333333333333, 1: 0.08333333333333333, 2: 0.25, 3: 0.4166666666666667} Sum: 0.8333333333333334 a = 0.16666666666666663 Full pmf: {0: 0.08333333333333333, 1: 0.08333333333333333, 2: 0.25, 3: 0.4166666666666667, 4: 0.16666666666666663} Total sum: 1.0 E[X] = 2.5 E[X^2] = 7.499999999999999 Var(X) = 1.2499999999999991 Var((1/a) X) = 44.999999999999986 [/PYTHON OUTPUT]
Reasoning Process

[THOUGHT] Using the computed value a = 1/6, we have Var(X) = 5/4, so Var((1/a)X) = Var(6X) = 36 * 5/4 = 45. \boxed{45}

Final Model Output
45

Comparative Analysis (P36) (Average across runs)

Avg Time Taken

Gemini-3-Pro-Preview
684.4
EXAONE-4.0.1-32B (high)
193.2
Deepseek-V3.2
67.4
Llama-VARCO-8B-Instruct
62.2
HCX-007(high)
36.9
Solar-Pro-2 (31B)(high)
34.2
A.X-4.0 (72B)
25.7
Claude-Opus-4.5
14.8
Grok-4.1-fast
9.0
GPT-5.1 (high)
8.3

Avg Token Usage

EXAONE-4.0.1-32B (high)
43263.0
Solar-Pro-2 (31B)(high)
6659.0
Gemini-3-Pro-Preview
5840.0
HCX-007(high)
4585.0
Grok-4.1-fast
3971.0
Claude-Opus-4.5
3958.0
Deepseek-V3.2
3770.0
GPT-5.1 (high)
2953.0
Llama-VARCO-8B-Instruct
2843.0
A.X-4.0 (72B)
2312.0