MHB How Is the Sampling Distribution of a Sample Mean Determined?

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SUMMARY

The sampling distribution of the sample mean is defined by the formula $$\bar{x}\sim N\left(\mu,\frac{\sigma}{\sqrt{n}}\right)$$ when the population standard deviation ($\sigma$) is known. In cases where $\sigma$ is unknown, the student-$t$ distribution should be utilized instead of the normal distribution. This distinction is crucial for accurately determining the sampling distribution and solving related statistical problems.

PREREQUISITES
  • Understanding of normal distribution and its properties
  • Knowledge of the Central Limit Theorem
  • Familiarity with student-$t$ distribution
  • Basic statistical concepts such as population mean ($\mu$) and standard deviation ($\sigma$)
NEXT STEPS
  • Study the Central Limit Theorem in depth
  • Learn about the properties and applications of the student-$t$ distribution
  • Explore practical examples of sampling distributions in real-world scenarios
  • Review statistical software tools for calculating sampling distributions, such as R or Python's SciPy library
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Students, educators, and professionals in statistics or data analysis who need a clear understanding of sampling distributions and their applications in hypothesis testing and confidence interval estimation.

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1. On this question I really have no idea how they got these answers so I just need someone to walk me through it step by step please

View attachment 42052. Part B on this question I don't know how to get the correct answer either

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In your first problem, you're talking about the samping distribution of the mean. If the standard deviation of the population is known, you can use the normal distribution; that is,
$$\bar{x}\sim N\left(\mu,\frac{\sigma}{\sqrt{n}}\right),$$
where $\mu$ is as given, $\sigma$ is the population standard deviation (also given in this case), and $n$ is the sample size. As a side note: in most real-world applications, you don't know $\mu$ or $\sigma$. Not knowing the mean isn't such a big deal - just approximate with $\bar{x}$. But if you don't know $\sigma$, then you have to use the student-$t$ distributions instead of the normal distribution.

So, now that you know the sampling distribution, can you work out the rest of the problem?
 

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