Confidence Intervals for Means Intro

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.

Find the Margin of Error to two decimal places.

• 1.90

• 1.89

• 1.899

• 1.99

A population has a standard deviation of σ = 17.3. How large of a sample must be drawn so that a 95% confidence interval for µ will have a Margin of Error equal to 1.4?

• 586.6

• 587

• 586

• 585

Find the Critical Value for an 86% Confidence Level.

• -1.48

• 1.48

• 1.282

• -1.47

Given the Critical Value of Z = 2.11, find the Confidence Level.

• 96.52%

• 0.9652

• .9826

• 98.26%

You are given two sets of data measuring the same information, both with the same sample size. Set A has a larger Standard Error than Set B. If you were looking for a 99.8% Confidence Interval, which set would have a larger Margin of Error?

• Set A

• Set B

• Not enough information

• I have no idea what you're asking me to do

The larger your confidence interval is, the more sure (higher confidence level) you can be.

• True

• False

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

• σ

• 25

• t*

• 2.064

• n

• 600

• x-bar

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.

Identify the Variables

• 2.40

• x-bar

• 12

• s

• 0.2

• t*

• 2.201

• n

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)

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