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1. In a survey, 19 people were asked how much they spent on their child's last birthday gift. The...

Question:

1. In a survey, 19 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $39 and standard deviation of $4. Construct a confidence interval at a 80% confidence level.

2.Express the confidence interval {eq}389.4 \pm 142 {/eq} in the form of a trilinear inequality.

3. Karen wants to advertise how many chocolate chips are in each Big Chip cookie at her bakery. She randomly selects a sample of 59 cookies and finds that the number of chocolate chips per cookie in the sample has a mean of 11.2 and a standard deviation of 2.8. What is the 99% confidence interval for the number of chocolate chips per cookie for Big Chip cookies?

4. You want to obtain a sample to estimate a population mean. Based on previous evidence, you believe the population standard deviation is approximately {eq}\sigma=22.6 {/eq} You would like to be 95% confident that your estimate is within 2 of the true population mean. How large of a sample size is required? Use a z* value accurate to TWO places for this problem. (Not z = 2)

Confidence interval:

The confidence interval for the population means provides the range for the population mean which can be calculated by adding and subtracting the margin of error from the sample mean. The margin of error shows the deviation from sample mean which is the product of critical value and the standard error.

Answer and Explanation:


1)

It is given that the sample size is 19, the sample mean is 39, the confidence level is 0.8, and the sample standard deviation is 4.

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Using the t Distribution to Find Confidence Intervals

from Statistics 101: Principles of Statistics

Chapter 9 / Lesson 6
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