20. Lightbulbs of a certain type are advertised as having an average lifetime of 750 hours. The price of these bulbs is very favorable, so a potential customer has decided to go ahead with a purchase arrangement 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 What conclusion would be appropriate for a signi cance level of .05? A signi cance level of .01?
What signi cance level and conclusion would you recommend?