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Finding Correct Z and T Scores for Confidence Intervals

Finding appropriate z- and t-scores is important when constructing confidence intervals. Confidence intervals allow one to estimate important population parameters such as population mean, population proportion, population standard deviation, etc. We will also study how confidence intervals will let one determine how large of a sample is required in order to get within a desired error range. Thus, confidence intervals offer important real-world applications. In Part 4 of this lab (described below) you will use a population mean confidence interval to determine if the local economy is sufficient to handle a new candy-making business.

Part 3, however, focuses on finding the correct z- and t-scores for a given confidence level. You should carefully follow the examples located inside the Conf Intervals worksheet in our Lab 6 Excel file (linked above or here). Then, answer the following questions. Note that these questions are also inside the worksheet.

1. Using Excel, find the z-score that corresponds to the following Confidence Levels:

a. 80%
b. 85%
c. 92%
d. 97%

2. Using Excel, find the t-score that corresponds to the following Confidence Levels and Sample Sizes:

a. 95% with n = 25
b. 96% with n = 15
c. 97% with n = 21
d. 91% with n = 10

Solution Preview

(1)We use the excel formula -NORMSINV

(a) -NORMSINV((1 - 0.80)/2) = 1.2816

(b) -NORMSINV((1 ...

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