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Confidence intervals for Proportion homework problems from 14-week course

Question 1 (Mandatory) (0.25 points)

What is the relationship between the confidence interval and the margin of error ?

Question 1 options:

	The confidence interval is half the width of the margin of error.
	The margin of error is twice the confidence interval.
	The confidence interval is twice the margin of error.
	None of these

Question 2 (Mandatory) (0.25 points)

Which of the following confidence levels will provide the widest intervals?

Question 2 options:

	99%
	85%
	95%
	90%

Question 3 (Mandatory) (1 point)

Question 3 options:

An internet service provider sampled 1000 of its customers, 189 of them experienced an interruption in high speed service during the previous month. Calculate the 99% confidence interval for the proportion of all customers that experienced an interruption in high speed service during that month. Round to 3 decimal places.

Lower limit =

Upper limit =

Question 4 (Mandatory) (0.5 points)

Write a summary statement for this confidence interval. Be sure to use the context of the problem.

Question 4 options:

Question 5 (Mandatory) (0.5 points)

A community college would like to estimate the percentage of their students that have children under 18 years old. They randomly select 450 students and ask them about having children and their children's ages. The 90% confidence interval for this situation is (24.5%, 31.5%)

Which statement below correctly summarizes the confidence interval?

Question 5 options:

	We are 90% confident that the percentage of all students at this community college that have children (<18yr) is 28%.
	We are 90% confident that the percentage of all students at this community college that have children (<18yr) is between 24.5% and 31.5%.
	There is a 90% chance that the percentage of students at this college that have children (<18yr) is between 24.5% and 31.5%.
	The chance a student will have children (<18yr) is between 24.5% and 31.5%.

Question 6 (Mandatory) (0.75 points)

A pollster wishes to estimate the true proportion of U.S. voters who oppose capital punishment. How many voters should be surveyed in order to be 90% confident that the true proportion is estimated to within 3.5%?

Question 6 options:

Question 7 (Mandatory) (1 point)

The confidence interval at the 95% level of confidence for the true population proportion was reported to be (0.665, 0.835). Which of the following is a possible 90% confidence interval from the same sample?

Question 7 options:

	(0.115, 0.335)
	(0.679, 0.821)
	(0.650, 0.825)
	(0.638, 0.862)

M3:L5

Confidence intervals for means questions from 14-week course.

Question 8 (Mandatory) (0.5 points)

In a random sample of 25 patients in the emergency room, the sample mean waiting time before being seen by a doctor was 28 minutes with a sample standard deviation of 6 minutes. Assume waiting times are approximately normal. Compute a 90% confidence interval for the mean waiting time for all patients to be seen by a doctor.

Question 8 options:

	(24.6, 31.4)
	(22, 28)
	(25.9, 30.1)
	(23, 33)

Question 9 (Mandatory) (0.5 points)

Write a summary statement for your confidence interval in question #1.

Question 9 options:

Question 10 (Mandatory) (0.5 points)

A random sample of high school students is used to estimate the mean time all high school students study for Geometry tests. A 95% confidence interval based on this sample is: 0.9 hours to 2.7 hours.

What is the sample mean ( )?

Question 10 options:

Question 11 (Mandatory) (0.5 points)

What is the margin of error (E)?

Question 11 options:

Question 12 (Mandatory) (1 point)

Question 12 options:

A survey about monthly cell phone service costs was given to 40 randomly selected Americans aged 25 – 64. Use the data to compute a 95% confidence interval for the mean amount all Americans aged 25 – 64 paid for cell phone service. Click here to open this data in StatCrunch.

Lower Confidence Limit =

Round to 2 decimal places.

Upper Confidence Limit =

Round to 2 decimal places.

Data table for cell service

Question 13 (Mandatory) (0.5 points)

Write a summary statement for your confidence interval in question #5.

Question 13 options:

Question 14 (Mandatory) (0.75 points)

How many commuters must be randomly selected to estimate the mean driving time of Baltimore commuters? We want 90% confidence that the sample mean is within 3 minutes of the population mean. Assume the population standard deviation is known to be 15 minutes.

Question 14 options:

	68 commuters
	1645 commuters
	17 commuters
	9 commuters

Question 15 (Mandatory) (0.5 points)

Saved

If we increase our sample size the width of the confidence interval will

Question 15 options:

	stay the same
	decrease
	increase