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## Chapter 8 - Day 9

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Overall Notes

• There is one version of this assessment provided in the Teacher Resources Materials (TRM). Use this assessment as-is or use it as a model to create your own.

• If you are making your own assessment, consider using the test bank and the ExamView software.

• Consider allowing students to use the four-step template from this lesson for a confidence interval.

• After returning graded quizzes to students, consider showing them the TInterval on the TI 83/84 calculator or using the One sample t interval for a mean applet at www.statsmedic.com/applets.

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Common Student Errors

• For the Normal/Large Sample condition, be sure that students are precise in their vocabulary. "the problem says it is normal" is not enough. We are looking for "the problem says that the population distribution is normal".

• For the Normal/Large Sample condition, be sure that students clearly identify the sample size and compare it to 30.

• When finding a critical value t* in Table B, students will sometimes forget to subtract 1 from the sample size to find the degrees of freedom (df).

• When finding a critical value t* in Table B, if there is a df that is not in the table (39 for example) students will sometimes incorrectly round to the nearest value (40). The preferred conservative approach here is to use df = 30.

• When calculating the margin of error for a confidence interval for a mean, students sometimes forget to multiply by the critical value t*.

• Students will sometimes skip parts of the 4-step process (like the specific formula). Insist that they show every part of the 4-step process.

• Students sometimes forget to include units when they are interpreting a confidence interval for a mean.

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