Math Problem Statement
A metropolitan courier business specializes in delivering business letters and other small packages from one large business district to another on the other side of a large city. Company leaders want to know which method of transportation is fastest along the 3-mile route that connects the two business districts. They decide to use 24 of their employees to determine the answer.
They randomly assign 13 of their employees to travel the 3-mile route as quickly as possible using an electric bicycle. The other 11 employees are randomly assigned to travel the same route using an electric scooter. A histogram of each sample is shown below.
Are the requirements met for finding a confidence interval or conducting a hypothesis test for the difference in mean travel time?
Two side-by-side bar charts compare travel times using bicycles (left) and scooters (right). Bicycle times peak in the middle, scooter times also peak in the middle.
Group of answer choices
No, while the sample sizes are large enough for the Central Limit Theorem to be applied, the samples were not randomly selected.
No, while the values from each sample were randomly selected, there is no indication that the distribution of mean travel times for scooter travel times is normally distributed. Further, the sample size is not large enough to apply the Central Limit Theorem.
No, while the values from each sample were randomly selected, there is no indication that either of the samples comes from a normal distribution.
Yes, the sample values were randomly selected and the distribution of sample mean differences is normal because the sample sizes are both large enough for the Central Limit Theorem to apply.
Yes, the sample values were randomly selected and the distribution of sample means for each population is normal because a histogram of each sample is approximately normal.
Yes, the sample values were randomly selected and the distribution of sample mean differences is normal because it was stated that the population of travel times was normal for both bicycles and scooters.
Solution
The correct answer is:
Yes, the sample values were randomly selected and the distribution of sample means for each population is normal because a histogram of each sample is approximately normal.
Explanation:
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Random Selection: The problem clearly states that the employees were randomly assigned to either the electric bicycle or electric scooter groups. This satisfies the requirement for random sampling.
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Normality: The histograms of both sample groups (bicycles and scooters) show that the data is approximately normal, as stated in the problem. For a hypothesis test or confidence interval for the difference in means, the sample distributions should ideally be normal or at least close to normal. The visual representation in the histograms suggests that both distributions are roughly symmetric, which is a good indicator of normality.
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Sample Size: Although the sample size for each group is not particularly large (13 for bicycles and 11 for scooters), it is generally accepted that if the sample sizes are greater than 30, the Central Limit Theorem would apply, even if the original distributions are not normal. Since the sample sizes here are smaller, we rely more on the histogram shape to determine normality. The histograms suggest that the data is not highly skewed, so it should be reasonable to proceed with inference about the means.
The other options are incorrect because:
- Option 1: The samples were indeed randomly selected, so this part of the statement is incorrect.
- Option 2: The histograms do show that the distributions of both sample groups are approximately normal, so this is not an issue here.
- Option 3: The histograms do suggest that the sample distributions are approximately normal.
- Option 4: This option talks about the Central Limit Theorem, but since we have histograms showing approximate normality, we don't need to rely on the Central Limit Theorem for smaller sample sizes here.
To recap:
- Randomness in selection is confirmed.
- Histograms suggest the distributions are roughly normal.
- The sample sizes, though small, do not hinder the ability to proceed with the analysis based on the histogram shape.
Let me know if you need further clarification or a deeper dive into any of these points!
Here are some follow-up questions to explore related concepts:
- How does the Central Limit Theorem apply when the sample size is small but the data is approximately normal?
- What assumptions should be checked before using a t-test for comparing means?
- How does one determine if a sample distribution is normal without a histogram (e.g., using a Q-Q plot)?
- Why is random sampling so important in statistical inference?
- How does sample size affect the power of a hypothesis test?
Tip: When you're unsure about the normality of data, always plot it! Histograms or Q-Q plots give a good visual cue about the underlying distribution.
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Math Problem Analysis
Mathematical Concepts
Statistics
Confidence Intervals
Hypothesis Testing
Normal Distribution
Central Limit Theorem
Formulas
None (conceptual question related to hypothesis testing and confidence intervals)
Theorems
Central Limit Theorem
Normality Assumption for Hypothesis Testing
Suitable Grade Level
Grades 11-12 (High School Statistics) or College-level Introductory Statistics
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