In an inertia welding experiment, a sample of 90 welds was tested. The sample me

Question

In an inertia welding experiment, a sample of 90 welds was tested. The sample mean and the sample standard deviation of the breaking strengths of these welds were found to be 89 ksi (thousand pounds per square inch) and 3.2 ksi, respectively.

(a) Construct a 90% confidence interval for the true mean breaking strength of such welds.

(b) Interpret the interval you constructed in Part (a) in the context of the problem.

(c) Construct a 99% confidence interval for the true mean breaking strength of such welds.

(d) Interpret the interval you constructed in Part (c) in the context of the problem.

Explanation / Answer

a) 90% c.i=Xbar+-Z(s/sqrt N-1)

=89+-1.65(3.2/sqrt 90-1)

=88.44 to 89.56

b) One can be 90% confident that true population mean breaking strength is between 88.44 Ksi to 89.56 Ksi.

c) 99% c.i=89+-2.58(3.2/sqrt 90-1)

=88.12 to 89.88

d) One can be 99% confident that true population mean breaking strength is between 88.12 Ksi to 89.88 Ksi.

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