Constructing a Confidence Interval for a Mean: STEP BY STEP

A random sample of 30 students at your school were asked how many hours of sleep they get on school nights. The average (sample mean) was 6.2 hours with a standard deviation of 1.3 hours.

We want to construct a 90% confidence interval for the true avg. number of hours all students sleep. What is the critical value for a 90% confidence interval?

• 1.31

• 2.042

• 2.457

• 1.697

A random sample of 30 students at your school were asked how many hours of sleep they get on school nights. The average was 6.2 hours with a standard deviation of 1.3 hours.

Interpret the 90% confidence interval in context

Which of these statements is true about a confidence interval?

• A larger sample size would make this interval narrower.

• A 99% confidence level would give a wider interval than a 95% one.

• If the standard deviation were larger, the confidence interval would be wider.

• The true average for the population is guaranteed to fall within this interval.

A random sample of 30 students at your school were asked how many hours they spend on extracurricular activities each week. The average (sample mean) was 5 hours with a standard deviation of 1.5 hours.

We want to construct a 99% confidence interval for the true avg. number of hours all students spend on extracurricular activities. What is the critical value for a 99% confidence interval?

• 2.660

• 2.75

• 2.326

• 2.57