Math Problem Statement

The lifetime of a certain type of battery is known to be normally distributed with standard deviation o = 17 hours. A sample of 50 batteries had a mean lifetime of 120.1 hours. It is desired to construct a 95% confidence interval for the mean lifetime for this type of battery. What is the point estimate? Find the standard error

Solution

Solution:

Step 1: Point Estimate

The point estimate for the population mean is the sample mean. In this case:

Point Estimate=xˉ=120.1hours.\text{Point Estimate} = \bar{x} = 120.1 \, \text{hours.}


Step 2: Standard Error of the Mean

The standard error (SE) of the sample mean is calculated using the formula:

SE=σn,SE = \frac{\sigma}{\sqrt{n}},

where:

  • σ=17\sigma = 17 (population standard deviation),
  • n=50n = 50 (sample size).

Substitute the values:

SE=1750.SE = \frac{17}{\sqrt{50}}.

First, calculate 50\sqrt{50}:

507.071.\sqrt{50} \approx 7.071.

Now calculate the standard error:

SE=177.0712.404.SE = \frac{17}{7.071} \approx 2.404.


Final Results:

  1. Point Estimate: 120.1120.1 hours.
  2. Standard Error: SE2.404SE \approx 2.404 hours.

Would you like help constructing the full confidence interval or understanding the steps in more detail?


Expanding Questions:

  1. How is the confidence interval calculated using the point estimate and standard error?
  2. What is the interpretation of a 95% confidence interval in this context?
  3. How does increasing the sample size affect the standard error and confidence interval?
  4. What if the population standard deviation was unknown? How would the method change?
  5. How can hypothesis testing be applied to determine if the true mean differs from a specific value?

Tip:

The standard error decreases as the sample size increases, leading to a narrower confidence interval and greater precision.

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Math Problem Analysis

Mathematical Concepts

Statistics
Confidence Intervals
Standard Error

Formulas

Point Estimate: \( \bar{x} = \text{sample mean} \)
Standard Error: \( SE = \frac{\sigma}{\sqrt{n}} \)

Theorems

Central Limit Theorem (for sample means)

Suitable Grade Level

Grades 11-12 or introductory college level