A company wanted to estimate the mean lifetime of its new model of lightbulbs. They use a method for testing bulbs that accelerates the process so the bulbs burn out relatively quickly, and the company can accurately calculate the corresponding lifetime under regular usage. They took a random sample of 555 of these new bulbs and calculated their lifetimes. Here are the data and summary statistics: Bulb 1 2 3 4 5
Lifetime 14.2 12.2 13.4 12.6 14.6
Mean= 13.4 years
Standard deviation= sx =1.02 years

Required:
Wrtite a 90% confidence interval for the mean lifetime in years) for this type of bulb.