Confidence Intervals Mean

Which confidence would result in a wider interval (assuming nothing else changed), 91% or 97%?

• 97%, z* is larger for higher confidence intervals

• 97%, the standard error is larger for higher confidence intervals

• 91%, z* is larger for lower confidence intervals

• 91%, the standard error is smaller for lower confidence intervals

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

• confidence interval, statistic

• point estimate, parameter

• point estimate, statistic

• confidence interval, parameter

Does the interval (3, 14) support the claim that the mean of a data set is 2.9

• Yes

• No

• Not enough information.

Increasing the sample size __________ the confidence interval. 

• increases

• decreases

• does not affect

• there is not enough evidence to determine the answer

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.

Identify the Variables

• 50

• t*

• 25

• x-bar

• 2.064

• σ

• 600

• n

You sample 12 bugs and find the sample mean is 2.40 cm. You are told the sample standard deviation is 0.2 cm. Find a 95% Confidence Interval.

• 12

• t*

• 2.40

• s

• 0.2

• x-bar

• 2.201

• n

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

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.

What is the Confidence Interval to one decimal place?

• (114.5, 125.6)

• (112.52, 127.68)

• (112.82, 127.38)

• (114.56, 125.64)

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.

• 1.699

• 0.56

• 0.537

• 19.325

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

• 2.807

• 2.508

• 2.064

• 2.819