business stats chap 8
A random sample of 81 automobiles traveling on a section of an interstate showed an average speed of 60 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph.
. become wider
Computing the necessary sample size for an interval estimate of a population proportion requires a planning value for . In case of any uncertainty about an appropriate planning value, we know the value that will provide the largest sample size for a given level of confidence and a given margin of error is _____.
.50
The t value with a 95% confidence and 24 degrees of freedom is _____.
2.064
A random sample of 25 statistics examinations was selected. The average score in the sample was 76 with a variance of 144. Assuming the scores are normally distributed, the 99% confidence interval for the population average examination score is _____.
69.29 to 82.71
A sample of 26 elements from a normally distributed population is selected. The sample mean is 10 with a standard deviation of 4. The 95% confidence interval for μ is _____.
8.384 to 11.616
A bank manager wishes to estimate the average waiting time for customers in line for tellers. A random sample of 50 times is measured and the average waiting time is 5.7 minutes. The population standard deviation of waiting time is 2 minutes. Which Excel function would be used to construct a confidence interval estimate?
CONFIDENCE.NORM
A manufacturer wants to estimate the proportion of defective items that are produced by a certain machine. A random sample of 50 items is selected. Which Excel function would NOT be appropriate to construct a confidence interval estimate?
STDEV
In order to estimate the average time spent on the computer terminals per student at a local university, data were collected from a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.2 hours. Refer to Exhibit 8-1. If the sample mean is 9 hours, then the 95% confidence interval is approximately _____.
c. 8.74 to 9.26 hours
To compute the minimum sample size for an interval estimate of μ when the population standard deviation is known, we must first determine all of the following EXCEPT _____.
degrees of freedom
An estimate of a population parameter that provides an interval believed to contain the value of the parameter is known as the _____.
interval estimate
In determining an interval estimate of a population mean when σ is unknown, we use a t distribution with _____ degrees of freedom
n-1
As the degrees of freedom increase, the t distribution approaches the _____ distribution.
normal
The general form of an interval estimate of a population mean or population proportion is the _____ plus or minus the _____.
point estimate, margin of error
The degrees of freedom associated with a t distribution are a function of the _____.
sample size
For the interval estimation of μ when σ is assumed known, the proper distribution to use is the _____.
standard normal distribution
The expression used to compute an interval estimate of μ may depend on any of the following factors EXCEPT _____.
whether there is sampling error
In general, higher confidence levels provide _____.
wider confidence intervals