=+unless it can be conclusively demonstrated that the true average lifetime is smaller than what is advertised. A random sample of 50 bulbs was selected, the lifetime of each bulb determined, and the appropriate hypotheses were tested using Minitab, resulting in the accompanying output:

Variable N Mean StDev SEMean Z P-Value lifetime 50 738.44 38.20 5.40 -2.14 0.016