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Course: AP??/College Statistics?>?Unit 9
Lesson 7: Sampling distributions for differences in sample means- Sampling distribution of the difference in sample means
- Mean and standard deviation of difference of sample means
- Shape of sampling distributions for differences in sample means
- Sampling distribution of the difference in sample means: Probability example
- Differences of sample means — Probability examples
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Mean and standard deviation of difference of sample means
Problem
A car manufacturer has two production plants in different cities. 皇冠足球体育 day, plant A produces of a certain type of car, while plant B produces of those cars. On average, all of these cars have a paint thickness of with a standard deviation of .
皇冠足球体育 day, quality control experts take separate random samples of cars from each plant and calculate the mean paint thickness for each sample. They then look at the difference between those sample means.
Consider the formula:
Why is it not appropriate to use this formula for the standard deviation of ?