In an inertia welding experiment, a sample of 50 welds were tested. The sample mean and sample standard deviation of the breaking strengths of these welds were found to be 94 ksi (thousand pounds per square inch) and 3 ksi, respectively.
(a) Construct a 95% condence interval for the true mean breaking strength of such welds.
(b) Construct a 99% condence interval for the true mean breaking strength of such welds.
(c) Is there evidence that the true mean breaking strength of such welds is less than 95 ksi?
Use the five ve-step hypothesis testing procedure in answering this question.