Clarifying the Concepts
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Calculating the Statistics
We use formulas to describe calculations. Find the error in each of the following formulas. Explain why each is incorrect and provide a correction.
For the data 93, 97, 91, 88, 103, 94, 97, calculate the standard deviation under both of these conditions:
For the data 1.01, 0.99, 1.12, 1.27, 0.82, 1.04, calculate the standard deviation under both of the following conditions. (Note: You will have to carry some calculations out to the third decimal place to see the difference in calculations.)
Identify the critical t value in each of the following circumstances:
Calculate degrees of freedom and identify the critical t value for a single-
Identify the critical t values for each of the following tests:
Assume we know the following for a two-
Assume we know the following for a two-
Students in a statistics course reported the number of hours of sleep they get on a typical weeknight. These data appear below.
5 6.5 6 8 6 6 6 7 5 7 6 6.5 7 6 7 4 8 6
Applying the Concepts
The relation between the z distribution and the t distributions: For each of the problems described below, which are the same as some of those described in Exercise 9.17, identify what the critical z value would have been if there had been just one sample and we knew the mean and standard deviation of the population:
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t statistics and standardized tests: On its Web site, the Princeton Review claims that students who have taken its course improve their Graduate Record Examination (GRE) scores, on average, by 210 points. (No other information is provided about this statistic.) Treating this average gain as a population mean, a researcher wonders whether the far cheaper technique of practicing for the GRE on one’s own would lead to a different average gain. She randomly selects five students from the pool of students at her university who plan to take the GRE. The students take a practice test before and after 2 months of self-
Single-
Consideration of Future Consequences and a dot plot: The following data are Consideration of Future Consequences (CFC) scores for 20, already arranged in order from lowest to highest:
Credit card debt and dot plots: Below are the amounts of credit card debt reported by 27 men and 23 women.
Putting It All Together
Paid days off and the single-
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Death row and the single-