=+35. An experiment was performed to compare the fracture toughness of high-purity Ni-maraging steel with commercial-purity steel of the same type. For 32 high-purity specimens, the sample mean toughness and sample standard deviation of toughness were 65.6 and 1.4, respectively, whereas for 32 commercialpurity specimens, the sample mean and sample standard deviation were 59.2 and 1.1, respectively. Estimate the difference between true average toughness for the high-purity