My Math Forum Confidence Intervals Help please!

 April 12th, 2010, 05:47 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, 01:54 AM #2 Math Team   Joined: Apr 2010 Posts: 2,778 Thanks: 361 Re: Confidence Intervals Help please! Hello mochisushi01, Rewrite the time in z-scores, using $z=\frac{\bar{X}-\mu}{\sigma}$. If you have a graphic calculator, you can find the point on the curve where surface on the left of that point = $\frac{1-0.97}{2}=0.015$. Or use a table. Hoempa

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