Confidence Intervals

Which of the following is the definition of a "point estimate?"

• The midpoint of the confidence interval

• The sample size

• The population

• The standard deviation

What is the point estimator for the interval (5 , 13)?

• 9

• 10

• 11

• 8

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 point estimate.

• 10

• 105.2

• .90

• 75

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 Critical Value for the mean.

• 1.67

• 1.28

• -1.67

• -1.28

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.

• (.59, .79)

• (.62, .85)

• (.60, .90)

• (.65, .87)

What is the point estimate, p̂, of this sample?

• .322

• .342

• .465

• .511

What is the margin of error of this sample?

• .21

• .344

• .14

• .342

The football coach randomly selected ten players and timed how long each player took to perform a certain drill. The times (in minutes) were: 13.2, 5.1, 7.5, 8.0, 12.7, 7.6, 13.8, 14.5, 7.7, and 10.5. Determine a 95 percent confidence interval for the mean time for all players.

• 12.42 < μ < 7.70

• 7.82 < μ < 12.30

• 7.70 < μ < 12.42

• 12.30 < μ < 7.82

Find the Critical Value for an 86% Confidence Level for a proportion.

• 1.48

• -1.48

• 1.96

• -1.96

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)

• (112.8, 127.4)

• (112.82, 127.38)

• (114.56, 125.64)