The following observations were made on fracture toughness of a base plate of 18% nickel maraging steel [“Fracture s 5 2.81 n 5 9 n 5 25 P(x2 , 14.611 or x2 . 37.652)

n 5 22 P(10.98 # x2 # 36.78)

n 5 10 n 5 10 x.995,25 2 x.99,25 2

x.005,25 2 x.01,25 2

x.1,25 2 x.1,15 2

Testing of Weldments,” ASTM Special Publ. No. 381, 1965:

328–356 (in ksi , given in increasing order)]:

69.5 71.9 72.6 73.1 73.3 73.5 75.5 75.7 75.8 76.1 76.2 76.2 77.0 77.9 78.1 79.6 79.7 79.9 80.1 82.2 83.7 93.7 Calculate a 99% CI for the standard deviation of the fracturetoughness distribution. Is this interval valid whatever the nature of the distribution? Explain.