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# Sample Size Determination

### Sample Size: Boxes

The mean weight is 20.4 pounds, the standard deviation .5 pounds. How many boxes must the processor sample to be 95 percent confident that the sample mean does not differ from the population mean by more than .2 pound?

### Sample Size to be 99% Confident of Accurate Results

A researcher would like to estimate the average age of physicians at a clinic. How large does the sample need to be if the researcher would like to be 99% confident that the estimate is accurate within one year. From a previous study, the standard deviation of age is known to be 3 years. Provide an interpretation of the results.

### American Water Works Association result analysis: sample size, one- or two-tailed test

The American Water Works Association estimates that the average person in the United States uses 123 gallons of water per day. Suppose some researchers believe that more water is being used now and want to test to determine whether it is so. They randomly select a sample of Americans and carefully keep track of the water use

### Sample Size: Noise Levels at Urban Hospitals

A researcher is interested in estimating the noise levels in decibels at area urban hospitals. She wants to be 99% confident that her estimate is correct. If the standard deviation is 4.4, how large a sample is needed to get the desired information to be accurate within 0.65 decibels? Show all work.

### Sample size: Nickel

A previous study of nickels showed that the standard deviation of the weight of nickels is 150 milligrams. How many nickels does a coin counter manufacturer need to weigh so that she can be 98% confident that her sample mean is with 25 milligrams of the true average weight of a nickel?

### Statistics: Sampling and Sampling distribution problems

Teamwork Unit 4 5-41, Suppose you are sampling from a population with mean µ=1,065 and standard deviation &#963;=500. The sample size is n=100. What are the expected value and the variance of the sample mean &#713;X? 5-44, When sampling is for a population proportion from a population with actual proportion p=0.5 using

### Client's mean income: What sample size for 95% and 99% level of confidence

A social service agency plans to conduct a survey to determine the mean income of its clients. The director of the agency prefers that you measure the mean income very accurately, to within + or - \$500 from a sample taken 2 years ago, you estimate that the standard deviation of income for this population is about \$5000 your job

### Sample Size Calculation: Estimate the Mean Weight Loss

A medical statistician wants to estimate the average weight loss of people who are on a new diet plan. In a preliminary study, he guesses that the standard deviation of the population of weight losses is about 10 pounds. How large of sample should he take to estimate the mean weight loss to within two pounds and with 90% confid

### Some stats problems

1. The amounts (in ounces) of juice in eight randomly selected juice bottles are: 15.4 15.7 15.2 15.8 15.8 15.4 15.0 15.6 Assuming the population of amounts in juice bottles is known to be normally distributed, create a 95% confidence interval estimate for &#61549;, the mean amount of juice in all bottles. You will b

### Sample Size and Population Mean

Q1: Why does the sample size play such an important role in reducing the standard error of the mean? What are the implications of increasing the sample size? Q2: Why might one be interested in determining a sample size before a study is undertaken? How do population variability and a level of certainty affect the size of

### Sample Size Calculation-High-Speed Internet Access

A researcher wishes to estimate with 99% confidence, the proportion of adults who have high-speed Internet access. Her estimate must be accurate within 2% of the true proportion. a) ind the minimum sample size needed, using a prior study that found that 36% of the respondents said they have high-speed Internet access. What

### Investor Deposits: Sample Size Calculation - Confidence Interval

An investment firm with 10,000 clients would like to accurately forecast the average dollar amount their current customer will deposit over the coming year. They decide to telephone a random selection of 25 of their customers to ask how much they plan to deposit, and they would like to keep this sample as small as possible so th

### Sample size for estimating a population proportion

The manager of a department store wants to determine what proportion of people who enter the store use the store's credit cards for their purchases. What size sample should he take so that at 95% confidence the error will not be more than 6%?

### Sample size calculation problem

9-30. Past surveys reveal that 30 percent of tourists going to Las Vegas to gamble during a weekend spend more than \$1,000. Management wants to update this percentage. a. The new study is to use the 90 percent confidence level. The estimate is to be within 1 percent of the population proportion. What is the necessary sample s

### Statistics - Minimal Sample Size Required

Managers at an automobile manufacturing plant would like to estimate the mean completion time for an assembly line. Assuming the standard deviation is 10.1 minutes, what is the minimal sample size for managers to be 99% confident that their estimate is within 2.2 minutes.

### Minimum Sample Size for Rental Car Prices

A consumer advocacy group is doing a large study on rental car prices....Using the value of 750 miles per month as the standard deviation, what is the minimum sample size needed in order for the consumer group to be 90% confident that is estimate within 175 miles per month...

### Sample size estimation for mean

An automobile manufacturer wants to estimate the mean gasoline mileage that its customers will obtain with its new compact model. How many sample runs must be performed in order that the estimate be accurate to within 0.25 mpg at 90% confidence? (Assume that &#963; = 2.0.)

### Understandanding sample sizes

If a population of ten thousand children what steps would you use to select a representative sample size of one hundred fifty? 1/2 boys and 1/2 girls 70% white and 30% nonwhite 57% single-parent family and 43% dual-parent family)

### Confidence Estimate and sample size

A researcher is interested in estimating the average salary of fire fighters in a large city. He wants to be 95% confident that his estimate is correct. If the standard deviation is \$1050, how large a sample is needed to get the desired information and to accurate within \$200?

### Sample Size

How I would obtain a 150 representative sample size?

### Statistics - Choosing Sample Size

Choosing an appropriate sample size A consumer advocacy group is doing a large study on car rental practices. Among other things, the consumer group would like to estimate the mean monthly mileage, u , of cars rented in the U.S. over the past year. The consumer group plans to choose a random sample of monthly U.S. rental car mi

### Sample Size for estimating population mean

In order to be accepted into a top university, applicants must score within the top 5% on the SAT exam. Given that SAT test scores are normally distributed with a mean of 1000 and a standard deviation of 200, what is the lowest possible score a student needs to qualify for acceptance into the university? A) 1330 B) 1400 C

### Sample size calculation explained in this answer

1. The Arkansas State Police wish to estimate the average mph being traveled on the interstate highways, which cross the state. If the estimate is to be within 8 mpg of the true mean with 98% confidence and the estimated standard deviation is 22 mph, how large a sample size must be taken? 2. The odds in favor of an event ar

### Audit of Coomes Molding

The firm of Le and Lysius was conducting the audit of Coomes Molding Corporation for the fiscal year ended October 31. Michelle Le, the partner in charge of the audit, decides that MUS (Monetary Unit Sampling, a form of Probability Proportional to Size (PPS) sampling) is the appropriate sampling technique to use in order to aud

### Average Cost of a 3 Minute Phone Call

You are interested in determining the average cost of a 3-minute telephone call to locations within the continental U.S. What sample size must you take to be 96% confident that the results will be within \$.75 of the true mean cost per call? From the phone company, you have received an estimate of = 7.71.

### Understanding the Formula for Optimal Sample Size

In Week 1 of RES/342 we determined the optimal sample size, n, using a three variable formula. Fill in the following table (see attachment) listing the three variables and specify the effect on n (either + or -) of increasing and decreasing each variable, one at a time.

### Finding Sample Size.

Sample Size for Weights of Quarters The Tyco Video Game Corporation finds that it is losing income because of slugs used in video games. The machines must be adjusted to accept coins only if they fall within set limits. In order to set these limits, the mean weight of quarters in circulation must be estimated. A sample of qu

### Sunroof and Side Air Bags. Find the sample size necessary to estimate a population proportion.

Toyota provides an option of a sunroof and side air bag package for its Corolla model. This package costs \$1400 (\$1159 invoice price). Assume that prior to offering this option package, Toyota wants to determine the percentage of Corolla buyers who would pay \$1400 extra for the sunroof and side air bags. How many Corolla buys

### Sample size problem set

Please see the attached file. A company wants to conduct a telephone survey of randomly selected voters to estimate the proportion of voters who favor a particular candidate in a presidential election, to within 2% error with 95% confidence. It is guessed that the proportion is 53%. 1. What is the required minimum sampl

### Sample Size Determination for an Insurance Company

1) In order to set rates, an insurance company is trying to estimate the number of sick days that full time workers at an auto repair shop take each year. A previous study indicated the standard deviation was 2.8 days. How large a sample must be selected if the company wants to be 95% confident that the true mean differs from th