Probability and Statistics for Engineering and the Sciences
9th Edition
ISBN: 9781305251809
Author: Jay L. Devore
Publisher: Cengage Learning
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Chapter 9, Problem 83SE
In an experiment to compare bearing strengths of pegs inserted in two different types of mounts, a sample of 14 observations on stress limit for red oak mounts resulted in a sample mean and sample standard deviation of 8.48 MPa and .79 MPa, respectively, whereas a sample of 12 observations when Douglas fir mounts were used gave a mean of 9.36 and a standard deviation of 1.52 (“Bearing Strength of White Oak Pegs in Red Oak and Douglas Fir Timbers,” J. of Testing and Evaluation, 1998, 109–114). Consider testing whether or not true average stress limits are identical for the two types of mounts. Compare df’s and P-values for the unpooled and pooled t tests.
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The tensile strength of paper using 5% hardwood and 10% hardwood are to be compared. A random sample of 41 sheets made from 5% hardwood had an average tensile strength of 1.52 lbs. with a standard deviation of 0.33 lbs. A random sample of 61 sheets made from 10% hardwood had an average tensile strength of 1.88 lbs. with a standard deviation of 0.42 lbs.
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There are many different properties of wood, for example, thermal conductivity, vapor permeance and air permeability. The dry density of wood is often used as a measure of shear strength. A study was conducted to compare the strengths of oriented strand board (OSB) and plywood. Independent random samples of each type of wood were obtained and the dry density of wood (in kg/m3) was measured.
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Chapter 9 Solutions
Probability and Statistics for Engineering and the Sciences
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