posted by Mike on .
A battery manufacturer is positive that its AA batteries last for 1,000 hours. However, you’re working for Consumer Reports and you don’t agree with what they say about their product. So, you buy 400 batteries and you test them out. Your findings are that the batteries last 990 hours on average with a standard deviation of 125. If you used a significance level of 1%, what is your opinion about the company’s batteries?