I was attempting a self-study question on Margin of Error and managed to get the answer right. The answer key states 2.77, but I managed to get at 2.76. Close enough I guess.
But I thought that it seems pretty weird that I did not have to use many of the provided variables such as mean or even the confidence interval.
Although I managed to get the right answer, I am not sure if I did really answer the question correctly. Appreciate some guidance please.
A portable DVD manufacturer based in Shanghai provides battery perfor- mance information in order to inform customers when making a purchasing decision. One of the important measures of battery performance is the length time average batteries last compared with a standard battery with a base of 100. This mean that a set of batteries with a grade of 200 should last consumers twice as long, on average, as a set of batteries graded with a base of 100. A Chinese manufacturer’s organization wants to estimate the actual battery life of brand-name batteries that claim to be graded 200. A random sample of n = 400 indicates a sample mean battery life of 195.3 and a standard deviation of 21.4. A 99% confidence interval for the population mean battery life for batteries produced by this manufacturer under this brand name is constructed. Find the margin of error in this estimation.