Problem Analysis #35

16.35s
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Problem Statement

A population is normally distributed with mean mm and standard deviation 55. From this population, a random sample of size 3636 is taken, and a 99%99\% confidence interval for the population mean mm is constructed using the sample mean. The resulting confidence interval is 1.2 $$\leq$$ m $$\leq$$ a. Find the value of aa. (Here, ZZ denotes a standard normal random variable, and use P(Z2.58)=0.99\text{P}(|Z| \leq 2.58) = 0.99.) [3 points]Compute 10a10a.\

Ground Truth
55
Execution Trace
Reasoning Process

[THOUGHT] To find the value of aa in the 99% confidence interval 1.2ma1.2 \leq m \leq a, we use the formula for the confidence interval of the population mean:

CI=xˉ±Zσn\text{CI} = \bar{x} \pm Z \cdot \frac{\sigma}{\sqrt{n}}

Given:

  • The lower bound of the interval is 1.21.2.
  • The population standard deviation σ=5\sigma = 5.
  • The sample size n=36n = 36.
  • The Z-score for 99% confidence is Z=2.58Z = 2.58.

The margin of error (ME) is calculated as:

ME=Zσn=2.5856=2.15\text{ME} = Z \cdot \frac{\sigma}{\sqrt{n}} = 2.58 \cdot \frac{5}{6} = 2.15

Since the confidence interval is symmetric around the sample mean xˉ\bar{x}, the sample mean is the midpoint of the interval:

xˉ=1.2+a2\bar{x} = \frac{1.2 + a}{2}

The lower bound of the interval is:

xˉME=1.2\bar{x} - \text{ME} = 1.2

Substituting xˉ\bar{x}:

1.2+a22.15=1.2\frac{1.2 + a}{2} - 2.15 = 1.2

Solving for aa:

1.2+a2=1.2+2.15=3.351.2+a=6.7a=6.71.2=5.5\frac{1.2 + a}{2} = 1.2 + 2.15 = 3.35 \\ 1.2 + a = 6.7 \\ a = 6.7 - 1.2 = 5.5

Thus, 10a=10×5.5=5510a = 10 \times 5.5 = 55. [/THOUGHT] [PYTHON]

Calculate the margin of error

Z = 2.58 sigma = 5 n = 36 ME = Z * (sigma / (n ** 0.5))

Lower bound of the interval

lower_bound = 1.2

Calculate the sample mean (midpoint)

sample_mean = lower_bound + ME

Calculate the upper bound 'a'

a = 2 * sample_mean - lower_bound

Compute 10a

result = 10 * a print(result) [/PYTHON]

Tool Output
[PYTHON OUTPUT] 55.00000000000001 [/PYTHON OUTPUT]
Reasoning Process

[THOUGHT] The Python output confirms that 10a=55.0000000000000110a = 55.00000000000001, which rounds to the integer 5555. This matches our earlier derivation. [/THOUGHT] \boxed{55}

Final Model Output
55

Comparative Analysis (P35) (Average across runs)

Avg Time Taken

EXAONE-4.0.1-32B (high)
636.4
Llama-VARCO-8B-Instruct
80.1
HCX-007(high)
49.6
Deepseek-V3.2
47.8
Gemini-3-Pro-Preview
24.4
Solar-Pro-2 (31B)(high)
16.4
Claude-Opus-4.5
13.8
A.X-4.0 (72B)
13.8
Grok-4.1-fast
10.6
GPT-5.1 (high)
7.8

Avg Token Usage

Llama-VARCO-8B-Instruct
6041.0
HCX-007(high)
5122.0
Gemini-3-Pro-Preview
4633.0
Solar-Pro-2 (31B)(high)
4521.0
Grok-4.1-fast
4352.0
A.X-4.0 (72B)
3481.0
Claude-Opus-4.5
3452.0
Deepseek-V3.2
2931.0
GPT-5.1 (high)
2481.0
EXAONE-4.0.1-32B (high)
1752.0