Margin Error Confidence Interval

Previous studies show that the standard deviation for work time is 3 hours, and a survey of 40 students has a mean of 9.8 work hours per week.

The 95% confidence interval is…

• (8.84, 10.76)

• (8.87, 10.73)

• (9.02, 10.58)

• (9.00, 10.60)

Suppose that a confidence interval for hours worked by students was computed to be (8.82, 10.78). Which of these is a valid interpretation of this confidence interval?

• There is a 95% probability that the average number of hours worked by all students is between 8.82 and 10.78 hours.

• There is a 95% probability that a randomly selected student worked between 8.82 and 10.78 hours.

• We are 95% confident that the population average number of hours worked by all students is between 8.82 and 10.78 hours.

• We are 95% confident that the average number of hours worked by the students in our sample is between 8.82 and 10.78 hours.

Which of the following equation is the correct one for finding the margin of error?

• a

• b

• c

• d

Which z-value is used for a 95% confidence interval?

• 1.65

• 1.96

• 2.58

• 2.33

Which z-value is used for a 90% confidence interval?

• 1.645

• 1.96

• 2.58

• 2.33

Which of the following equation is the correct one for finding the confidence interval?

• a

• b

• c

• d

What is the S in this equation?

• mean or average

• Z-score

• Standard deviation

• Sample size

What is the n in this equation?

• mean or average

• Z-score

• Standard deviation

• Sample size

In a crash test of 15 troopers, collision repair costs are found to have a distribution that is approximately normal, with a mean of $1800 and a sample standard deviation of $950. Construct a 99% confidence interval for the repair cost. 

• (1069.77, 2530.23)

• (1077.13, 2522.87)

• (1167.15, 2432.85)

• None of these.

A sample of 40 people owned an average of 1.35 apple products. It is known from a previous study that the population standard deviation of apple product ownership is 0.63 products. Construct a 95% confidence interval.

• (1.11, 1.58)

• (1.15, 1.55)

• (1.19, 1.51)

• (1.09, 1.61)