Exam 9: Estimation and Confidence Intervals

Sugar is packaged in 16 ounce bags. To test the weight of the bags, a few were checked. The mean weight was 15.95 ounces; the standard deviation, 0.5 ounces. How many bags must the processor sample to be 99 percent confident that the sample mean does not differ from the population mean by more than 0.2 ounces?

To calculate the sample size required to estimate a population mean, we must know or estimate the ______________ of the population distribution.

A pharmaceutical company wanted to estimate the population mean of monthly sales for their 250 sales people. Forty sales people were randomly selected. Their mean monthly sales was $10,000 with a population standard deviation of $1000. Construct a 95% confidence interval for the population mean.

A silkscreen printing company purchases t-shirts. To ensure the quality of the shipment, 300 t-shirts are randomly selected. 15 are defective. What is the estimated proportion defective in the population?

A sample mean is the best point estimate of

How is the t distribution similar to the standard z distribution?

A confidence interval is narrower when the sample size __________________.

One factor in determining the size of a sample is the degree of confidence selected. This is usually 0.95 or 0.99, but it may be any degree of confidence you specify.

Mileage tests were conducted on a randomly selected sample of 100 newly developed automobile tires. The results showed that the average tread life was 50,000 miles with a standard deviation of 3,500 miles. What is the best estimate of the average tread life in miles for the entire population of these tires?

A company wants to estimate next years total revenue. Why is an interval estimate preferred to a point estimate?

The 95 percent confidence interval states that 95 percent of the sample means of a specified sample size selected from a population will lie within plus and minus 1.96 standard deviations of the hypothesized population mean.

The distribution of Student's t has

A bank wishes to estimate the mean credit card balance owed by its customers. The population standard deviation is estimated to be $300. If a 98 percent confidence interval is used and an interval of $75 is desired, how many customers should be sampled?

A survey of an urban university (population of 25,450) showed that 870 of 1100 students sampled supported a fee increase to fund improvements to the student recreation center. Using the 95% level of confidence, what is the confidence interval for the proportion of students supporting the fee increase?

To calculate the sample size required to estimate a population mean, smaller margins of error require ______________ sample sizes.

An interval estimate is a range of values used to estimate a population parameter.

The t distribution is similar to the z distribution in all BUT one of the following characteristics. Which one is it?

A university wants to determine the proportion of students who use a cash card to pay at the university food service. Out of 100 students surveyed, 65 students use a cash card. Estimate the value of the population proportion.

A population is estimated to have a standard deviation of 25. We want to estimate the population mean within 2, with a 95 percent level of confidence. How large a sample is required?

The distribution of Student's t is