AP Statistic Confidence Interval for Means

What interval should be used?

• 2 Sample t interval for means

• Paired t interval

• Paired t test

• 1 proportion z interval

A sample of 25 Ohio students who have taken the ACT have a sample mean score of 21.  What is the critical value used to build a 95% confidence interval for the true mean ACT score for all Ohio students?

• 2.064

• 2.086

• 1.96

• 2.060

What test should be used?

• 2 proportion z test

• 1 proportion z test

• 2 sample t test for means

• 1 sample t test for mean

A __________ gives an interval of plausible values for the _____________. 

• confidence interval, statistic

• point estimate, parameter

• point estimate, statistic

• confidence interval, parameter

Estimate the average number of pinecones that a 30-year-old pine tree produces each year.  Fifty-five pine trees were observed over a one-year period. Which procedure is appropriate?

• t interval for means

• t test for means

• z interval for proportions

• z test for proportions

An amusement park owner is considering changing her model from "pay for each ride" to "one fee for all rides."  She observes 2000 guests to see if they spend less than the $30 fee that she intends to put into place. Which procedure is appropriate?

• t interval for means

• t test for means

• z interval for proportions

• z test for proportions

Increasing the sample size __________ the confidence interval. 

• increases

• decreases

• does not affect

• there is not enough evidence to determine the answer

A sample of 20 cupcakes found the interval for average calories to be (150, 350). Which is the correct interpretation of the 95% confidence interval?

• We are 95% confident that the true mean caloric content can be found with a sample of 150 to 350 cupcakes.

• We are 95% confident that the interval (150, 350) captures the true average caloric content.

• We are 95% confident that a sample of 20 cupcakes will find 250 calories per cupcake.

• None of these are correct.

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 standard deviation of $950. Construct a 99% confidence interval for the repair cost for the population.

• (1070, 2530)

• (1273, 2326)

• (1799, 1801)

• (1776, 1823)

The lifetime of a certain type of batter is known to be normally distributed with a standard deviation of 20 hours. A sample of 50 batteries had a mean lifetime of 120.1 hours. It is desired to construct a 99% confidence interval for the mean lifetime of this type of battery. What is the Confidence Interval to one decimal place?

• (114.5, 125.6)

• (112.8, 127.4)

• (112.82, 127.38)

• (114.56, 125.64)