Chapter 1.1, Problem 10ES

they take? 8.1.13 WP GO Tutorial An article in the Journal of Agricultural Science ["The Use of Residual Maximum Likelihood to Model Grain Quality Characteristics of Wheat with Variety, Climatic and Nitrogen Fertilizer Effects” (1997, Vol. 128, pp. 135–142)] investigated means of wheat grain crude protein content (CP) and Hagberg falling number (HFN) surveyed in the United Kingdom. The analysis used a variety of nitrogen fertilizer applications (kg N/ha), temperature (°C), and total monthly rainfall (mm). The following data below describe temperatures for wheat grown at Harper Adams Agricultural College between 1982 and 1993. The temperatures measured in June were obtained as follows: 15.2 14.2 14.0 12.2 14.4 12.5 14.3 14.2 13.5 11.8 15.2 Assume that the standard deviation is known to be σ = 0.5. a. Construct a 99% two-sided confidence interval on the mean temperature. b. Construct a 95% lower-confidence bound on the mean temperature. c. Suppose that you wanted to be 95% confident that…

1 S 0 sin(lnx) x² - 1 Inx dx

8.1.1 WP For a normal population with known variance σ², answer the following questions: - a. What is the confidence level for the interval x — 2.140/ √√n≤≤+2.140/√√n?

8.1.8 A civil engineer is analyzing the compressives trength of concrete. Compressive strength is normally distributed with σ2 = 1000(psi)2. A random sample of 12 specimens has a mean compressive strength ofx  = 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 found in part (a). 8.1.9Suppose that in Exercise 8.1.8 it is desired to estimate the compressive strength with an error that is less than 15 psi at 99% confidence. What sample size is required?

8.1.12 Ishikawa et al. [“Evaluation of Adhesiveness of Acinetobacter sp. Tol 5 to Abiotic Surfaces,” Journal of Bioscience and Bioengineering (Vol. 113(6), pp. 719–725)] studied the adhesion of various biofilms to solid surfaces for possible use in environmental technologies. Adhesion assay is conducted by measuring absorbance at A590. Suppose that for the bacterial strain Acinetobacter, five measurements gave readings of 2.69, 5.76, 2.67, 1.62, and 4.12 dyne-cm2. Assume that the standard deviation is known to be 0.66 dyne-cm2. a. Find a 95% confidence interval for the mean adhesion. b. If the scientists want the confidence interval to be no wider than 0.55 dyne-cm2, how many observations should they take?

Answer questions 8.2.1 and 8.2.2 respectively

8.2.3 A research engineer for a tire manufacturer is investigating tire life for a new rubber compound and has built 16 tires and tested them to end-of-life in a road test. The sample mean and standard deviation are 60,139.7 and 3645.94 kilometers. Find a 95% confidence interval on mean tire life. 8.2.4  Determine the t-percentile that is required to construct each of the following one-sided confidence intervals: a. Confidence level = 95%, degrees of freedom = 14 b. Confidence level = 99%, degrees of freedom = 19 c. Confidence level = 99.9%, degrees of freedom = 24

8.1.6The yield of a chemical process is being studied. From previous experience, yield is known to be normally distributed and σ = 3. The past 5 days of plant operation have resulted in the following percent yields: 91.6, 88.75, 90.8, 89.95, and 91.3. Find a 95% two-sided confidence interval on the true mean yield. 8.1.7 .A manufacturer produces piston rings for an automobile engine. It is known that ring diameter is normally distributed with σ = 0.001 millimeters. A random sample of 15 rings has a mean diameter of x = 74.036 millimeters. a. Construct a 99% two-sided confidence interval on the mean piston ring diameter. b. Construct a 99% lower-confidence bound on the mean piston ring diameter. Compare the lower bound of this confi- dence interval with the one in part (a).

8.1.2 .Consider the one-sided confidence interval expressions for a mean of a normal population. a. What value of zα would result in a 90% CI? b. What value of zα would result in a 95% CI? c. What value of zα would result in a 99% CI? 8.1.3 A random sample has been taken from a normal distribution and the following confidence intervals constructed using the same data: (38.02, 61.98) and (39.95, 60.05) a. What is the value of the sample mean? b. One of these intervals is a 95% CI and the other is a 90% CI. Which one is the 95% CI and why?