Question

In a study of academic procrastination, the authors of a paper reported that for a sample of 411 undergraduate students at a midsize public university preparing for a final exam in an introductory psychology course, the mean time spent studying for the exam was 7.44 hours and the standard deviation of study times was 3.30 hours. For purposes of this exercise, assume that it is reasonable to regard this sample as representative of students taking introductory psychology at this university.

(a) Construct a 95% confidence interval to estimate *μ*,
the mean time spent studying for the final exam for students taking
introductory psychology at this university. (Round your answers to
three decimal places.)

( , )

(b) The paper also gave the following sample statistics for the
percentage of study time that occurred in the 24 hours prior to the
exam.

* n* =
411

Construct a 90% confidence interval for the mean percentage of
study time that occurs in the 24 hours prior to the exam. (Round
your answers to three decimal places.)

( , )

Interpret the interval.

We are confident that 90% of the mean percent of study time that occurs in the 24 hours prior to the exam for all students taking introductory psychology at this university is within this interval.We are confident that the mean percent of study time that occurs in the 24 hours prior to the exam for all students taking introductory psychology at this university is within this interval at least 90% of the time. We are 90% confident that the mean percent of study time for all students taking introductory psychology is within this interval.We are 90% confident that the mean percent of study time that occurs in the 24 hours prior to the exam for all students taking introductory psychology at this university is within this interval.

Answer #1

a) At 95% confidence level, the critical value is
z_{0.025} = 1.96

The 95% confidence interval is

b) At 90% confidence level, the critical value is
z_{0.05} = 1.645

The 90% confidence interval is

We are 90% confident that the mean percent of study time that occurs in the 24 hours prior to the exam for all students taking introductory psychology at this university is within this interval.

In a study of academic procrastination, the authors of a paper
reported that for a sample of 421 undergraduate students at a
midsize public university preparing for a final exam in an
introductory psychology course, the mean time spent studying for
the exam was 7.44 hours and the standard deviation of study times
was 3.30 hours. For purposes of this exercise, assume that it is
reasonable to regard this sample as representative of students
taking introductory psychology at this university....

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