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# Confidence Interval

### Confidence Interval Question for Houses Sold

Suppose that a random sample of fifteen recently sold houses in a certain city has a mean sales price of \$290000 , with a standard deviation of \$15,000 . Under the assumption that house prices are normally distributed, find a 90% confidence interval for the mean sales price of all houses in this community. Then complete the tabl

### Confidence interval for the ratio of population variances

Confidence interval for the ratio of population variances Actuaries use various parameters when evaluating the cost of a life insurance policy. The variance of the life spans of a population is one of the parameters used for the evaluation. Each year, the actuaries at a particular insurance company randomly sample 25 people wh

### Hypothesis and confidence intervals

(1) A sample of 49 observations is taken from a normal population with a standard deviation of 10. The sample mean is 55. Determine the 99 percent confidence interval for the population mean. (5) A research firm conducted a survey to determine the mean amount steady smokers spend on cigarettes during a week. They found the di

### Confidence Interval - comparative study

In a comparative study of two new drugs, A and B, 300 patients were treated with drug A, and 200 patients were treated with drug B. (The two treatment groups were randomly and independently chosen.) It was found that 204 patients were cured using drug A and patients were cured using drug B. Let P1 be the proportion of the popul

### Solution to "Statistics - Confidence Interval" question

A random sample of 200 bolts from machine A contained 14 defective bolts, while an independently chosen, random sample of 325 bolts from machine B contained 35 defective bolts. Let P1 be the proportion of the population of all bolts from machine A that are defective, and let P2 be the proportion of the population of all bolts fr

### Confidence Interval-difference between means (small sample)

The university data center has two main computers. The center wants to examine whether computer 1 is receiving tasks that require processing times comparable to those of computer 2. A random sample of 10 processing times from computer 1 showed a mean of 69 seconds with a standard deviation of 15 seconds, while a random sample of

### 1. What is the lower limit of the 90% confidence interval? 2. What is the upper level of the 90% confidence interval?

To determine the possible effect of a chemical treatment on the rate of seed germination, 300 chemically treated seeds and 250 untreated seeds were sown. It was found that 267 of the chemically treated seeds and 205 of the untreated seeds germinated. Let P1 be the proportion of the population of all chemically treated seeds that

### 1. What is the lower limit of the 99% confidence interval? 2. What is the upper limit of the 99% confidence interval?

In random, independent samples of 200 adults and 400 teenagers who watched a certain television show, 134 adults and 272 teens indicated that they liked the show. Let P1 be the proportion of all adults watching the show who liked it, and let P2 be the proportion of all teens watching the show who liked it. Find a 99% confidence

### 1. What is the lower limit of the 90% confidence interval? 2. What is the upper limit of the 90% confidence interval?

According to the historical data, the life expectancy in the United States is less than the life expectancy in Ireland. A new study has been made to see whether this has changed. Records of 210 individuals from the United States who died recently are selected at random. The 210 individuals lived a mean of 77.5 years with a stand

### Confidence Interval

According to the historical data, the life expectancy in the United Kingdom is less than the life expectancy in the United States. A new study has been made to see whether this has changed. Records of 230 individuals from the United Kingdom who died recently are selected at random. The 230 individuals lived a mean of 78.2 years

### Finding confidence interval for mean

Consider the following random sample of diameter measurements (in inches) of 12 softballs. 4.9 4.71 4.84 4.7 4.78 4.79 4.82 4.76 4.72 4.88 4.73 4.68 If we assume that the diameter measurements are normally distributed, find a 95% confidence interval for the mean diameter of a

### Confidence Interval

The lifetime of a certain brand of battery is known to have a standard deviation of 11.5 hours. Suppose that a random sample of 70 such batteries has a mean lifetime of 43.3 hours. Based on this sample, find a 90% confidence interval for the true mean lifetime of all batteries of this brand. Then complete the table below. 1.

### The Sony corporation produces a Walkman that requires two AA Batteries. The mean life of these batteries in this product is 35.0 hours. The distribtion of the battery lives closely follows the normal probability distribtion with a standard deviation of 5.5 hours. As a part of their testing program Sony tests samples of 25 batteries. (1) What is the standard error of the distribution of the sample mean? (2) What proportion of the samples will have a mean useful life of more than 36 hours?

The Sony corporation produces a Walkman that requires two AA Batteries. The mean life of these batteries in this product is 35.0 hours. The distribtion of the battery lives closely follows the normal probability distribtion with a standard deviation of 5.5 hours. As a part of their testing program Sony tests samples of 25 batter

### Sample Size, Margin of error

I) Find the minimum sample size you should use to assure that your estimate of p will be within the required margin of error around the population p. 1) margin of error:0.01; confidence level:95%; from a prior study p is estimated by the decimal equivalent of 55%. 2) Margin of error: 0.007; confidence level: 98%; p and q u

### Confidence Interval & Sample standard deviation

A 90% confidence interval runs from 65.891 to 70.109 for the mean daily number of credit card applications that are rejected from a computer system and must be handled manually. The confidence interval was obtained from a sample of 45 randomly selected days that had a sample mean of 68. What is the sample standard deviation?

### Confidence Interval for mean for time speed..

1. A sample of 100 elementary school children revealed that the average number of hours per week spend watching TV for the sample was 18.5 hours with a standard deviation equal to 2.5 hours. Find a 90% confidence interval for the mean time spend watching TV for the population from which the sample was selected.

### Calculation of confidence interval

Using the Central Limit Theorem. In Exercises 5-8, assume that women's height are normally distributed with a mean given by µ = 63.6 in. and a standard deviation given by &#963; = 2.5 (based on data from the National Health Survey). Sect. 6-5, p. 287 (For these problems, see examples on p. 283, 284 #5. a. If 1 wo

### Confidence interval estimation evaluation

You are involved in the evaluation of viewer ship of television shows for your local TV station. You have been tasked to determine a 95% confidence interval for the viewing of a show called 'CSI Phoenix'. You have randomly queried 400 local adults and determined that 150 of them watched the last episode of the show. >> create a

### Solving the Confidence Interval for the Mean

A recent survey of 50 executives who were laid off from their previous position revealed it took a mean of 26 weeks for them to find another position. The standard deviation of the sample was 6.2 weeks. Construct a 95 percent confidence interval for the population mean. Is it reasonable that the population mean is 28 weeks?

### How to choose an appropiate sample size

Managers at an automobile manufacturing plant would like to estimate the mean completion time of an assembly line operation, u. The managers plan to cheese a random sample of completion times and estimate u via the sample. Assuming that the standard deviation of the population of completion times is 10.4 minutes, what is the min

### Sample size for estimating a population mean

An estimate is needed of the mean acreage of farms in Manitoba, Canada. The estimate should be correct to within 100 acres with probability 0.95. A preliminary study suggests that 500 acres is a reasonable guess for the standard deviation of farm size. How large a sample of farms is required and given that random sample size

### Confidence Interval

Dave the jogger runs the same route every day (about 2.2 miles). On 18 consecutive days, he recorded the number of steps using a pedometer. The results were 3450 3363 3228 3360 3304 3407 3324 3365 3290 3289 3346 3252 3237 3210 3140 3220 3103 3129 Construct a 90 percent confidence interval for the true me

### Confidence interval estimation for regression coefficients

1 What is the R^2 Value for your regression equation? 2 What is the value of the coefficient of Blue Collar in your equation? 3 What is the lower limit of the 95% CI for this coefficient? 4 What is the upper limit of the 95% CI for this coefficient?

### Statistics

A supervisor for a large company wishes to estimate the proportion of parts from a supplier that are defective. He has selected a random sample of n = 200 incoming parts and has found 11 to be defective. Based on a 95% confidence level, the upper and lower limits for the confidence interval estimate are approximately 0.0234 to 0

### Confidence interval and Hypothesis testing problems

Question 1: Confidence Interval for Effects of Marijuana Use on College Students: Data: Items sorted correctly by light marijuana users: n = 64, x = 53.3, s = 3.6 Items sorted correctly by heavy marijuana users: n = 65, x = 51.3, s = 4.5 Q: Refer to the sample data above and construct a 98% confidence interval fo

### Statistics

8.64 Biting an unpopped kernel of popcorn hurts! As an experiment, a self-confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the unpopped kernels were counted. There were 86. (a) Construct a 90 percent confidence interval for the proportion of all kernels that would n

### Confidence Interval for the True Mean

8.48 A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below: 0 26

### Confidence Intervals and Mean Chloride Level

A laboratory in Florida is interested in finding the mean chloride level for a healthy resident in the state. A random sample of 70 healthy residents has a mean chloride level of 102 mEg/L. If it is known that the chloride levels in healthy individuals residing in Florida have a standard deviation of 35 mEg/L find a 90% confiden

### Confidence Intervals - House Prices

Please solve attached. Suppose that a random sample of fourteen recently sold houses in a certain city has a mean sales price of \$280,000, with a standard deviation of \$9000. Under the assumption that house prices are normally distributed, find a 90% confidence interval for the mean sales price of all houses in this community

### Confidence interval 97%

36. The American Restaurant Association collected information on the number of meals eaten outside the home per week by young married couples. -A survey of 60 couples showed the sample mean number of meals eaten outside the home was 2.76 meals per week, -with a standard deviation of 0.75 meals per week. Answer the followi