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Confidence Interval

Confidence Interval of Automobile Shop Managers

An automobile shop manager timed six employees and found the average time it took then to change a water pump was 18 minutes. The standard deviation of the sample was 3 minutes. Find the 99% confidence interval of the true mean, and how would you explain the interval to the average layperson

Hypothesis Testting, Confidence Intervals and Levels of Significance

In a statistics lecture, students are asked whether or not they enjoyed doing statistics. Random sample of 50 students was taken and 30 of them said that they enjoyed doing statistics. The lecturer claimed that more than 50% of the students enjoyed doing statistics. (i) Test, at the 5% level of significance, whether or not

Confidence Intervals and Standard Deviation

In a manufacturing process, the diameter of the steel rods is the product characteristic. A random sample of 25 steel rods is taken and sample mean is 8.88 cm. The diameter is assumed to be normally distributed with standard deviation 1.25. (i) Find a 95% confidence interval for the true diameter. If the standard deviation

Confidence Interval

A random sample of 172 students was asked to rate on a scale to from 1 (not important) to 5 (extremely important) health benefits as a job characteristic (note that the rating scale can also have decimals, i.e. a student can give a rating of 1.32). The sample mean rating was 3.31, and the sample standard deviation was 0.70.

Confidence Interval

What is meant by confidence interval? Please explain with real life examples.

Statistics - Confidence interval for mean and proportion

1. Find the critical value za/2 which corresponds to a degree of confidence of 98%. 2. Express the confidence interval in the form of p-hat plus or minus E. -0.052 < p < 0.568 3. Find the margin of error for the 95% confidence interval used to estimate the population proportion if n = 175 and x = 95. 4. Find the mini

Mean/Standard Deviation

See attached file for full problem description. 1. The Internal Revenue Service is studying contributions to charity. A random sample of 36 returns is selected. The mean contribution is $150 and the standard deviation of the sample is $20. Construct a 98 percent confidence interval for the population mean. 2. A manufactu

Confidence interval for mean and proportion

11. As part of a safety check, the Pennsylvania Highway Patrol randomly stopped 65 cars and checked their tire pressure. The sample mean was 32 pounds per square inch with a sample standard deviation of 2 pounds per square inch. Develop a 98 percent confidence interval for the population mean. 12. A survey of 4,000 colleg

Confidence Interval Question

Assume a mean 0f 110 and a standard deviation of 10 in a population, a. What proportion of the population has levels greater than 115 and less than 105? b. If repeated sample of 30 were selected, what proportion of them would have less than 100?

Estimates and sample size, estimating population variance

1. In considering the production of a new car accessory, the Michigan Manufacturer Company wants to do a marketing study to determine the proportion of cars with cellular phones. How many cars must be sampled to have 92% confidence that the sample proportion is in error by no more than 0.03? The answer is 851 need help setting

Statistics Equations

1. Explain how the purpose of estimation differs from the purpose of a hypothesis test. 2. Explain why it would not be reasonable to use estimation after a hypothesis test for which the decision was "fail to reject Ho." 3. Explain how each of the following factors affects the width of a confidence interval: a. Increasing

Percentage of Men

Give the z-value, percentage and/or the number of men we would expect to meet these criteria. Ignore the approximation adjustment. What percentage of men would we expect to be over 200 pounds? What percentage of men would we expect to be under 180 pounds? What percentage of the men would we expect to be within 15 pou

Confidence Interval

The number of hours that a network server was down each month of the previous year is: 4, 4, 5, 1, 5, 1, 1, 2, 1, 2, 1, 2. Place a 95% confidence interval about the population mean number of down hours per month. My thoughts: mean = 29 / 12 = 2.4167 mean + Z(0.025) * s/sqrt(n) mean - Z(0.025) * s/sqrt(n)

Population mean, sample size, sample mean

1. An upper-level sociology class at a large urban university has 120 students, including 34 seniors, 57 juniors, 22 sophomores and 7 freshmen. a). Imagine that you choose one random student from the classroom (perhaps by using a random number table). What is the probability that the student will be junior? b). What is the pro

What is the confidence interval?

CycleTime 67.696 56.684 64.118 53.158 66.609 Question 66.623 47.507 What is the confidence interval for the Cycle Time? 76.022 67.497 38.815 59.449 49.47 51.259 55.991 44.522 89.973 66.651 54.697 77.258 18.505 58.354 24.056 50.781 84.328 70.17 66.169 48.589 65.022 40.901

Information about "Confidence Interval for proportion"

From a large number of actuarial exam scores, a random sample of 375 scores is selected, and it is found that 270 of these 375 are passing scores. Based on this sample, find a 99% confidence interval for the proportion of all scores that are passing. Then complete the table below. Carry your intermediate computations to at le

Confidence Interval for the Mean

Call Center 1 Call Center 2 19.14 20.64 24.59 27.42 28.37 25.68 27.17 20.45 29.52 18.55 18.97 23.91 24.53 22.84 29.33 22.33 18.42

Laid Off Employees due to Illness

Investigate the rate at which employees with an illness where laid off; a survey of 100 people was conducted. 7 were laid off b/s of the illness. I have to construct a 90% confidence interval for the true percentage all that were laid off to their illness.

Confidence interval for true average degree of polymerization

Question: An article contained the following observations on degree of polymerization for paper specimens for which viscosity times concentration fell in a certain middle range. Degree: 429 421 421 422 425 427 431 436 437 439 446 447 448 452 453 463 465 a) Calculate a two-sided 98% confidence interval for

Upper and Lower Confidence Limits

A journal article reports that a sample of size 5 was used as a basis for calculating a 95% confidence interval for the true average natural frequency (Hz) of delaminated beams of a certain type. The resulting interval was [216.3, 217.8] You decide that a confidence level of 99% is more appropriate than the 95% level used. Hint

Confidence Interval Questions

A confidence interval is desired for the true average stray-load loss (watts) for a certain type of induction motor when the line current is held at 10 amps for a speed of 1500 rpm. Assume that stray-load loss normally distributed with sigma = 2.3 Give answer to three decimal places. Compute a 95% confidence interval f

Confidence Intervals for Seats in an Employee Lounge

The seats in the employee lounge are made for discomfort so employees will not stay long. The mean duration for 35 employees would stay in the lounge is 30 minutes. Suppose that we have &#963; = 33 minutes. Now, determine a 95% confidence interval for the mean duration of time, &#956;, spent in the lounge. (also attached

Confidence Interval for difference in means

A random sample of 40 men drank an average of 20 cups of coffee per week during finals, while a sample of 30 women drank an average of 15 cups of coffee per week. The sample standard deviations were 6 cups for the men and 3 cups for the women. The standard error for the difference between the two sample means is 1.095. Calcul

Confidence interval for mean of breaking strength

Consider the trash bag problem. Suppose that an independent laboratory has tested trash bags and has found that no 30-gallon bags that are currently on the market have a mean breaking strength of 50 pounds or more. On the basis of these results, the producer of the new, improved trash bag feels sure that its 30-gallon bag will b

Confidence Intervals and Significance Levels

68. In a study, Germination and Emergence of Broccoli, conducted by the Department of Horticulture at Virginia Polytechnic Institute and State University, a researcher found that at 5°C, 10 seeds out of 20 germinated, while at 15°C, 15 out of 20 seeds germinated. Compute a 95% confidence interval for the difference between t

Confidence Interval: Breaking Strengths of Cables

The breaking strengths of cables produced by a certain manufacturer have a standard deviation of 82 pounds. A random sample of 150 newly manufactured cables has a mean breaking strength of 1950 pounds. Based on this sample, find a 95% confidence interval for the true mean breaking strength of all cables produced by this manufact