Finding Confidence Intervals for Mean and Proportions

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 Standard Error.

• 75

• 10

• 105.2

• 1.155

A study found that in a sample of 44 subjects, 9 of agree that children under 6 shouldn’t be taken to nice restaurants. The 95% confidence interval for p is (0.082, 0.318). Interpret this interval.

• 95% of the time the proportion of people who believe children under 6 shouldn't be taken to nice restaurants will be between 8.2% and 31.8%.

• The population proportion of people who believe children under 6 shouldn't be taken to nice restaurants is between 8.2% and 31.8%.

• The probability that the proportion of people who believe children under 6 shouldn't be taken to nice restaurants will be between 8.2% and 31.8% is 95%.

• Based on this sample, I am 95% confident that the proportion of people who believe children under 6 shouldn't be taken to nice restaurants is between 8.2% and 31.8%.

A preliminary study suggests that 87% of people agree on an issue. How large must your sample size be so you could be within ± 3% of p calculate at 90% confidence?

• 7

• 466

• 5

• 338

Find the critical value, z*, for 91% confidence.

• 70

• 34

• 0.18

• -34

Find the critical value, z* for 97%

• 1.88

• 2.17

• -1.88

• -2.17

What is the margin of error of this sample?

• 0.28

• 0.14

• 0.342

• 0.684

If 827 represents "no" voters out of 2584, construct a 95% confidence interval for the "no" group.

• [.300,.340]

• [.298,.342]

• [.302,.338]

• [.288,.352]

A 90% confidence interval for the mean speed driven by cars on Due West Road is given by (21, 45). What was the sample mean (point estimate) of this study?

• 12

• 24

• 33

• None of these.

If a study on the average time spent on homework by high school students results in a 95% Confidence Interval of (114.56, 125.54) hours per year, then is it likely that the true average time µ spent on homework by all high school students is greater than 130 hours per year?

• Yes

• No

• Not enough information

• I have no idea what you're asking of me

Find the value of Z star for a 90% confidence interval.

• -1.96 

• 1.645

• 1.440

• -1.598