1 Thickness Strength 2.4066 4.9175 2.1328 4.8067 2.5937 5.1246 5 2.1933 4.7555 6 2.4579 4.7233 7 2.0665 4.3934 8 2.1994 4.4609 9 2.4575 4.7377 10 2.6724 4.3407 11 2.2738 4.9487 12 2.5392 4.4265 13 2.7956 4.3583 14 2.1228 4.5608 15 2.2055 4.8207 16 2.4359 4.7769 17 2.3353 5.2468 18 2.3238 4.8706 19 2.5267 4.5138 20 2.2146 4.4402 21 2.2699 4.6548 2 3
6 A valve manufacturer produces a butterfly valve composed of two semicircular plates on a
common spindle that is used to permit flow in one direction only (seen here:
http://en.wikipedia.org/wiki/Butterfly_valve). The semicircular plates are supplied by a vendor
with specifications that the plates be 2.37 millimeters thick and have a tensile strength of five
pounds per millimeter. A random sample of 20 such plates is taken. Electronic calipers are used
to measure the thickness of each plate. A universal testing machine was used to test the tensile
strength. The sample data are found in homework 5.xlsx.
a. Find point estimates of the thickness and tensile strength data. Compare with the
specifications.
b. Construct a 95% confidence interval for mean thickness. Draw conclusions regarding the
specification relative to the confidence interval.
c. Construct a 95% confidence interval for mean tensile strength. Draw conclusions
regarding the specification relative to the confidence interval.
d. Construct a 95% confidence interval for the standard deviation of tensile strength.
e. Construct a 95% confidence interval for the proportion of plates whose thickness is
greater than the specification.
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