stat 1a. A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with o2 = 1000(psi)2. A random sample of 12specimens has a mean compressive strength of x = 3250 psi.(a) Construct a 95% two-sided confidence interval on mean compressive strength.(b) Construct a 99% two-sided confidence interval on mean compressive strength. Compare the width of this confidence interval with the width of the one foundin part (a).Edit View InsertFormatToolsTable

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Answered: A civil engineer is analyzing the…

MATLAB: An Introduction with Applications

6th Edition

ISBN:9781119256830

Author:Amos Gilat

Publisher:Amos Gilat

Chapter1: Starting With Matlab

Section: Chapter Questions

Problem 1P

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A large multi-branch bank is affiliated with both the MasterCard and Visa credit cards. For a random sample of 100 MasterCard cardholders, it is observed that the average month-end account balance is R682.58 with a sample standard deviation of R307.05. For a random sample of 100 Visa cardholders, the average month-end account balance is R550.55 with a sample standard deviation of R265.29. The 90% confidence interval for the mean difference between the month-end account balances for the two types of credit card holders (rounded to three decimals) is:
A soft-drink manufacturer purchases aluminum cans from an outside vendor. A random sample of 70 cans is selected from a large shipment, and each is tested for strength by applying an increasing load to the side of the can until it punctures. Of the 70 cans, 52 meet the specification for puncture resistance. a) Find a 95% confidence interval for the proportion of cans in the shipment that meet the specification. b) Find a 90% confidence interval for the proportion of cans in the shipment that meet the specification. c) Find the sample size needed for a 95% confidence interval to specify the proportion to within ±0.05. d) Find the sample size needed for a 90% confidence interval to specify the proportion to within ±0.05. e) If a 90% confidence interval is computed each day for 300 days, what is the probability that more than 280 of the confidence intervals cover the true proportions?
Find the critical value, t c, used for a 97% confidence interval for the mean with a sample size of 33. Round to three decimal places. Provide the positive critical value.
A study was carried out on the blood pressure of 60-year-old women with glaucoma. In the study, 200 60-year-old women with glaucoma are randomly selected and their mean systolic blood pressure sample is 140 mmHg and the sample standard deviation is 25 mmHg. (a) Calculate a 90% confidence interval for the true mean systolic blood pressure in the population of 60-year-old women with glaucoma. (b) Suppose the study above was based on 100 women instead of 200, but the sample mean (140) and the standard deviation (25) are the same. Recalculate the 90% confidence interval. The gap gets wider or narrower? Why?
To study the effect of curing temperature on shear strength of a certain rubber compound, 80 specimens were cured at 150°C and 95 were cured at 130°C. The specimens cured at 150°C had an average shear strength of 620 psi, with a standard deviation of 20 psi. Those cured at 130°C had an average shear strength of 750 psi, with a standard deviation of 30 psi. Find a 95% confidence interval for the difference between the mean shear strengths of specimens cured at the two temperatures.
Past experience has indicated that the breaking strength of yarn used in manufacturing drapery material is normally distributed and that σ = 3 psi. A random sample of 8 specimens is tested, and the average breaking strength is found to be 95 psi. Find a 95% two-sided confidence interval on the true mean breaking strength. Round the answers to 1 decimal place.
The admissions officer at a small college compares the scores on the Scholastic Aptitude Test (SAT) for the school's in-state and out-of-state applicants. A random sample of 88 in-state applicants results in a SAT scoring mean of 1180 with a standard deviation of 41. A random sample of 17 out-of-state applicants results in a SAT scoring mean of 1107 with a standard deviation of 53. Using this data, find the 95% confidence interval for the true mean difference between the scoring mean for in-state applicants and out-of-state applicants. Assume that the population variances are not equal and that the two populations are normally distributed. Step 1 of 3: Find the critical value that should be used in constructing the confidence interval. Round your answer to three decimal places. Step 2 of 3: Find the standard error of the sampling distribution to be used in constructing the confidence interval. Round your answer to the nearest whole number. Step 3 of 3: Construct the 95% confidence…
A 30 month study is conducted to determine the difference in rates of accidents per month between two departments in an assembly plant. If a sample of 12 from the first department averaged 12.3 accidents per month with a standard deviation of 3.5, and a sample of 9 from the second department averaged 7.6 accidents per month with standard deviation of 3.4, find: The t-value for a 95% confidence interval is:
A company that produces white bread is concerned about the amount of sodium in its bread. The company takes a simple random sample of 100 slices of bread and computes the sample mean to be 103 milligrams of sodium per slice with a standard deviation of 10 milligrams. Construct a 99% confidence interval for the unknown mean sodium level.

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