Question

The following observations were made on fracture toughness of a base plate of 18% nickel maraging steel (in ksiin., given in increasing order)]: 65.2 71.9 72.8 73.1 73.1 73.5 75.5 75.7 75.8 76.1 76.2 76.2 77.0 77.9 78.3 79.6 79.7 79.9 80.1 82.2 83.7 93.5 Calculate a 99% CI for the standard deviation of the fracture toughness distribution. (Round your answers to one decimal place.) (C . ksiin Is this interval valid whatever the nature of the distribution? Explain. The interval is always valid. The distribution needs to be skewed to the right. The distribution needs to be approximately uniform. The distribution needs to be approximately normal. You may need to use the appropriate table in the Appendix of Tables to answer this question.

Answer 1

The software output for this problem is:

Parameter SEM N Value 5.396 1.150 22 4.326 to 7.263 4.151 to 7.711 3.843 to 8.724 90% Cl of the SD 95% CI of the SD 99% Cl of the SD

Hence,

99% confidence interval will be:

(3.8, 8.7)

Option D is correct.