Confidence Interval for Means

A 90% confidence interval for the mean speed driven by cars on East Main St. is given by (21, 45). What was the margin of error of this study?

• 12

• 24

• 33

• None of these.

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

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

• We are 95% confident that the true mean calorie content in cupcakes is between 150 and 350 calories.

• 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. 

• (1070, 2530)

• (1273, 2326)

• (1799, 1801)

• None of these.

The 90% interval for a statistics test was given by 72 +- 7. What is the lower bound for the interval?

• 7

• 72

• 65

• 79

A 90% confidence interval for the mean speed driven by cars on East Main St. is given by (21, 45). What was the sample mean of this study?

• 12

• 24

• 33

• None of these.

Find the t* value for a 99% confidence interval with a sample of 23 people.

• 1.714

• 1.711

• 2.064

• None of these.

I randomly select 25 students’ Math SAT scores and find the mean to be 600. I know the standard deviation of the population is 50. Find a 95% Confidence Interval.

• 95% confident the sample mean is between 580.4 and 619.6

• 95% confident the population mean is between 583.55 and 616.45

• 95% confident the population mean is between 579.36 and 620.64

• 95% confident the population mean is between 574.2 and 625.8

A sample of 30 women finds the mean height to be 62.3 in and the standard deviation to be 1.5 in. Find the margin of error of women's heights with a 95% confidence level.

• 699

• 0.56

• 0.537

• 19.325

When we say we have a 90% confidence interval, what are we 90% confident of?

• That the population mean is within the interval boundaries

• That the population mean is outside the interval boundaries

• That the sample mean is within the interval boundaries

• That the sample mean is outside the interval boundaries

The 90% interval for the Chapter 7 statistics test has a point estimate of 72% and a margin of error of 7%. What is the lower bound for the interval?

• 7%

• 72%

• 65%

• 79%