A sample of 150 brand A blade emitters showed a mean lifetime of 1400 hours and a standard deviation of 125 hours. A sample of 175 brand B blade emitters showed a mean lifetime of 1200 hours and a standard deviation of 80 hours.
i. Find the 95% confidence interval for the difference of mean lifetime of the populations of brands A and B.
ii. Find the 99% confidence interval for the difference of mean lifetime of the populations of brands A and B.
iii. At 5% significance level is there sufficient evidence to warrant concluding a significant difference between the mean lifetimes of the populations of brands A and B? Using the confidence interval method, show the steps of your hypothesis test.