Question 444206
Any help you can give me on these problems will be greatly appreciated.
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All of your problems are essentially the same.
You need a "sample mean"(x-bar) and you need a "margin of error"(ME).
The sample mean is provided by the problem narrative.
The ME = z*s/sqrt(n) where z depends on the level of confidence,
s is the standeard deviation (usually given) and n is the sample size.
The Confidence Interval is (x-bar - ME) < u < (x-bar + ME)
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1)
The new Twinkle bulb has a standard deviation 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be 500 hours. 
(a. Find the margin of error E for a 95% confidence interval. Round your answer to the nearest hundredths.
ME = z*s/sqrt(n)
ME = 1.96*35/sqrt(50) = 9.7015
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(b. Construct a 95% confidence interval for the mean life, mu of all Twinkle bulbs.
500-9.7015 < u < 500+9.7015
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Cheers,
Stan H.