Problem Analysis #36

14.82s
3,958 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] Let me solve this step by step.

First, I need to find the value of aa using the fact that the sum of all probabilities must equal 1.

For x=0,1,2,3x = 0, 1, 2, 3:

  • P(X=0)=2(0)112=112P(X = 0) = \frac{|2(0) - 1|}{12} = \frac{1}{12}
  • P(X=1)=2(1)112=112P(X = 1) = \frac{|2(1) - 1|}{12} = \frac{1}{12}
  • P(X=2)=2(2)112=312P(X = 2) = \frac{|2(2) - 1|}{12} = \frac{3}{12}
  • P(X=3)=2(3)112=512P(X = 3) = \frac{|2(3) - 1|}{12} = \frac{5}{12}

And P(X=4)=aP(X = 4) = a.

The sum must equal 1: 112+112+312+512+a=1\frac{1}{12} + \frac{1}{12} + \frac{3}{12} + \frac{5}{12} + a = 1

Then I need to compute V(1aX)=1a2V(X)V\left(\frac{1}{a}X\right) = \frac{1}{a^2}V(X).

Let me calculate this using Python. [/THOUGHT] [PYTHON] from fractions import Fraction

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

probs = {} for x in range(4): probs[x] = Fraction(abs(2*x - 1), 12) print(f"P(X = {x}) = {probs[x]}")

Sum of probabilities for x = 0, 1, 2, 3

sum_probs = sum(probs.values()) print(f"\nSum of P(X=0) to P(X=3) = {sum_probs}")

Find a

a = 1 - sum_probs print(f"a = P(X = 4) = {a}") probs[4] = a

Verify sum = 1

total = sum(probs.values()) print(f"Total probability = {total}")

Calculate E(X)

E_X = sum(x * probs[x] for x in range(5)) print(f"\nE(X) = {E_X}")

Calculate E(X^2)

E_X2 = sum(x**2 * probs[x] for x in range(5)) print(f"E(X^2) = {E_X2}")

Calculate V(X) = E(X^2) - (E(X))^2

V_X = E_X2 - E_X**2 print(f"V(X) = {V_X}")

Calculate V((1/a)X) = (1/a^2) * V(X)

V_result = V_X / (a**2) print(f"\nV((1/a)X) = V(X) / a^2 = {V_result}") print(f"V((1/a)X) as decimal = {float(V_result)}") [/PYTHON]

Tool Output
[PYTHON OUTPUT] P(X = 0) = 1/12 P(X = 1) = 1/12 P(X = 2) = 1/4 P(X = 3) = 5/12 Sum of P(X=0) to P(X=3) = 5/6 a = P(X = 4) = 1/6 Total probability = 1 E(X) = 5/2 E(X^2) = 15/2 V(X) = 5/4 V((1/a)X) = V(X) / a^2 = 45 V((1/a)X) as decimal = 45.0 [/PYTHON OUTPUT]
Reasoning Process

[THOUGHT] The calculation shows that:

  • The probabilities for x = 0, 1, 2, 3 are 1/12, 1/12, 1/4, 5/12 respectively
  • The constant a = 1/6
  • E(X) = 5/2
  • E(X²) = 15/2
  • V(X) = 5/4
  • V((1/a)X) = V(X)/a² = (5/4)/(1/36) = (5/4) × 36 = 45

The answer is 45. [/THOUGHT]

\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