An experiment was performed to compare the fracture toughness of high-purity 18 ni maraging steel with commercial-purity steel of the same type. for m = 30 specimens, the sample average toughness was x = 63.3 for the high-purity steel, whereas for n = 38 specimens of commercial steel y = 57.6. because the high-purity steel is more expensive, its use for a certain application can be justified only if its fracture toughness exceeds that of commercial-purity steel by more than 5. suppose that both toughness distributions are normal.