It's proposed that the average life expectancy these days is 76.5, but recent data suggests it might be more than that.
A sample size of 78 countries found a sample mean life expectancy of 80.5 years with a standard deviation of 9.2 years.
You want to formulate and test a hypothesis that can be used to challenge the validity of the claim at a significance level of 0.001.
With hypotheses H₀ :μ≤76.5 vs H₁​:μ>76.5, what is/are the critical value(s)?