AP Statistics Confidence Intervals

Jamal wants to know the percent of people in Phoenix that support recycling. He calls a random sample of 115 people and finds that 110 of them support recycling. Can he calculate a confidence interval?

• Yes, all conditions are met.

• No, the sample was not randomly collected

• No, the sample is not independent.

• No, the sampling distribution is not normal.

Ramon wants to know the percent of people in Arizona plan to go to a spring training baseball game this year. He calls a random sample of 200 Arizonans and finds that 25 plan to go to a game. Can he calculate a confidence interval?

• Yes, all conditions are met.

• No, the sample was not randomly collected

• No, the sample is not independent.

• No, the sampling distribution is not normal.

In a survey of 104 students, it was found that 79 went to the homecoming game this year. Calculate a 99% confidence interval for p.

• (0.652, 0.868)

• (0.691, 0.829)

• (0.678, 0.842)

• (0.685, 0.895)

A sample of 400 racing cars showed that 80 cars cost over $700,000. What is the 99% confidence interval of the true proportion of cars costing over $700,000?

• 0.001 < p < 0.005

• 0.566 < p < 0.693

• 0.148 < p < 0.252

• 0.023 < p < 0.045

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. What is the point estimate?

• 75

• 105.2

• 10

• 0.90

Given the interval (1.2, 1.8), what is the point estimate and the margin of error? 

• 1.5, 0.6

• 1.5, 0.3

• 1.2, 0.3

• 1.2, 0.6

What can you do to reduce the margin of error? 

• increase the confidence level

• decrease the confidence level

• increase sample size

• decrease sample size

What is the critical value z* for a 99% confidence interval? 

• -2.58

• 1.96

• -1.64

• 2.58

Using the same data, Hank calculated a 95% confidence interval and Maria calculated a 99% confidence interval. Which interval is wider?

• Hank's

• Maria's

• They used the same data so they are the same width.

• Cannot be determined.

Which of the following values below represents the critical value for a 98% confidence interval for p?

• 2.326

• 2.054

• 1.645

• 3.091