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April 12th, 2010, 04:47 PM  #1 
Newbie Joined: Apr 2010 Posts: 1 Thanks: 0  Confidence Intervals Help please!
Can someone show me how to do this problem? A manufacturer claims that it's light bulbs have a mean lifetime of 1550 hours with a standard deviation of 75 ours. A random sample of 50 bulbs is selected for testing. If the sample produces a mean of 1435.8 hours, is there sufficient evidence to reject the manufacturer's claim? Use alpha = .01. Find the 97% confidence interval of the population, "u" Please and thank you! 
April 13th, 2010, 12:54 AM  #2 
Math Team Joined: Apr 2010 Posts: 2,778 Thanks: 361  Re: Confidence Intervals Help please!
Hello mochisushi01, Rewrite the time in zscores, using . If you have a graphic calculator, you can find the point on the curve where surface on the left of that point = . Or use a table. Hoempa 

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