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April 12th, 2010, 04:47 PM   #1
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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!
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April 13th, 2010, 12:54 AM   #2
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Re: Confidence Intervals Help please!

Hello mochisushi01,

Rewrite the time in z-scores, 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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