Confidence Intervals

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% CL.

• 1.699
• 0.56
• 0.537
• 19.325

Tags

CCSS.HSS.IC.B.4

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

• 7
• 72
• 65
• 79

Tags

CCSS.HSS.IC.B.4

Which of the following does NOT have an affect on the width of a confidence interval?

• Sample mean
• t*
• Sample standard deviation
• Sample size

Which of the following changes to a study would result in a narrower confidence interval?

• increasing the confidence level, increasing the sample size
• decreasing the confidence level, decreasing the sample size
• increasing the confidence level, decreasing the sample size
• decreasing the confidence level, increasing the sample size.

Tags

CCSS.HSS.IC.B.4

Why do we use a t-distribution instead of a z-distribution for means? 

• It reflects greater variability present in small samples.
• It allows us to decrease the margin of error without increasing our confidence level.
• It allows us to use the population standard deviation.
• None of these.

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.

Tags

CCSS.HSS.IC.A.1

CCSS.HSS.IC.B.4

CCSS.HSS.ID.A.4

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

• 1.714
• 1.711
• 2.064
• None of these.

A research group wishes to estimate the mean amount of time (in hours) that members of a fitness center spend exercising each week. They want to estimate the mean within a margin of error of 0.5 hours with a 95% level of confidence. Previous data suggests that the standard deviation of the population is 2.2. Which of the following is the smallest sample size they could use?

• 60
• 75
• 90
• 180

Tags

CCSS.HSS.IC.A.1

CCSS.HSS.IC.B.4

A 90% confidence interval for a population mean is determined to be 800 to 900. If the confidence is increased to 95% confidence while the sample statistics and sample size remain the same, the confidence interval

• becomes wider
• becomes narrower
• does not change

Tags

CCSS.HSS.IC.B.4

A random sample of 100 visitors to a popular theme park spent an average of $142 on the trip with a standard deviation of $47.5. Which of the following would be the 98% confidence interval for the mean money spent by all visitors to this theme park?

• ($130.77, $153.23)
• ($132.77, $151.43)
• ($132.69, $151.31)
• ($140.88, $143.12)

Tags

CCSS.HSS.IC.A.1

CCSS.HSS.IC.B.4

CCSS.HSS.ID.A.4