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Exam 8: Interval Estimation

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Question 31

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A population has a standard deviation of 25. A random sample of 125 items from this population is selected. The sample mean is determined to be 325. At 95% confidence, the margin of error is

A) 2.24.
B) 5.
C) 4.38.
D) 11.18.

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Question 32

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In order to estimate the average time spent per student on the computer terminals at a local university, data were collected for a sample of 64 business students over a one-week period. Assume the population standard deviation is 1.6 hours. If the sample mean is 9 hours, then the 95% confidence interval is _____ hours.

A) 7.04 to 10.96
B) 7.36 to 10.64
C) 7.80 to 10.20
D) 8.608 to 9.392

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Question 33

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We can use the normal distribution to make confidence interval estimates for the population proportion, p, when​

The z value for a 97.8% confidence interval estimation is

The use of the normal probability distribution as an approximation of the sampling distribution of is based on the condition that both np and n(1 - p) equal or exceed​

To compute the necessary sample size for an interval estimate of a population proportion, all of the following procedures are recommended when p is unknown except​

In interval estimation, as the sample size becomes larger, the interval estimate

A random sample of 49 statistics examinations was taken. The average score, in the sample, was 84 with a variance of 12.25. The 95% confidence interval for the average examination score of the population of the examinations is

From a population with a variance of 484, a sample of 256 items is selected. At 95% confidence, the margin of error is

For a given confidence level and when σ is known, the margin of error in a confidence interval estimate

The degrees of freedom associated with a t distribution are a function of the​

In a random sample of 100 observations, = .2. The 95% confidence interval for p is

In general, higher confidence levels provide

As the degrees of freedom increase, the t distribution approaches the _____ distribution.

A random sample of 25,000 ACT test takers had an average score of 21 with a standard deviation of 5. What is the 95% confidence interval of the population mean?

From a population that is not normally distributed and whose standard deviation is not known, a sample of 6 items is selected to develop an interval estimate for the mean of the population (μ) .

When the level of confidence decreases, the margin of error

As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution

As the sample size increases, the margin of error

A 95% confidence interval for a population mean is determined to be 100 to 120. For the same data, if the confidence coefficient is reduced to .90, the confidence interval for μ