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The following observations were made on fracture toughness of a base plate of 18% nickel maraging steel (in ksi W, given in increasing order)]: 65.4 71.9 72.6 73.1 73.2 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 83.6 93.7 Calculate a 99% CI for the standard deviation of the fracture toughness distribution. {Round your answers to one decimal place.) (:.:)ksim Is this interval valid whatever the nature of the distribution? Explain. O The distribution needs to be skewed to the right. The distribution needs to be approximately normal. 0 The distribution needs to be approximately uniform. O The interval is always valid