Question 1169774
Ho: outcomes are the same
Ha: they are not
alpha p{reject Ho|Ho true}=0.01
test is a z 0.995, 
critical value is |z|>2.576
calculation z=(40-43)/9/sqrt(80)
z=-3sqrt(80)/9
=2.98
reject Ho p-value 0.0029 The mean lifetime of the light bulbs differs from 43 months.