Confidence Intervals for Means Intro

A sample of 30 women finds the mean height 62.3 in and the standard deviation 1.5 in. Find the margin of error of women's heights with a 95% CL. Round your critical value to 3 decimals.

• 1.699

• 0.56

• 0.537

• 19.325

In a crash test of 55 troopers, collision repair costs were found to have an approximately normal distribution, with a mean of $1800 and a standard deviation of $950. Using the formula, construct a 99% confidence interval for the repair cost. Round your critical value to 3 decimals and your interval to 2 decimals.

• (1470.02, 2129.98)

• (1373.65, 2326.69)

• (1799.02, 1801.54)

• None of these.

What is the critical value (z-score) for a 99% confidence interval? Round to 3 decimals.

• 2.326

• 1.96

• 1.645

• 2.576

An IQ test was given to a simple random sample of 75 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college. What is the point estimate?

• 75

• 105.2

• 10

• 0.90

The lifetime of a certain type of battery 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.

Using your calculator, 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)

Given the interval (1.2, 1.8), what is the point estimate and the margin of error? 

• 1.5, 0.6

• 1.5, 0.3

• 1.2, 0.3

• 1.2, 0.6

What is the margin of error for the interval (6.8, 12.9)?

• 9.85

• 3.05

• 3.50

• 6.8

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)