Original hypothesis: Ho: the strength has not been significantly improved after the improved process.

Because the population standard deviation is constant, the measured data n= 100 is a large sample, so the standard normal statistic z is taken.

Z = √n*(u-uo)/σ

Where σ = 1. 19, n = 100, uo = 6.

At present, the significance level is α=0.05, and the statistical critical value is Z(0.05), that is, the corresponding quantile when the probability of standard normal distribution is 0.95, which is known from the table as 1.645.

The actual statistical value obtained by bringing u = 6.35 into the Z statistic is 2.94 >: 1.645, so it is in the hypothetical negative domain.

Therefore, we can reject the assumption that our strength has been significantly improved.