SOLUTION: Can someone please help me solve this and explain why? Thank you The lifetime of a certain brand of battery is known to have a standard deviation of 10.5 hours. Suppose that a r

Question 185452: Can someone please help me solve this and explain why? Thank you
The lifetime of a certain brand of battery is known to have a standard deviation of 10.5 hours. Suppose that a random sample of 120 such batteries has a mean lifetime of 40.9 hours. Based on this sample, find a 95% confidence interval for the true mean lifetime of all batteries of this brand.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The lifetime of a certain brand of battery is known to have a standard deviation of 10.5 hours. Suppose that a random sample of 120 such batteries has a mean lifetime of 40.9 hours. Based on this sample, find a 95% confidence interval for the true mean lifetime of all batteries of this brand.
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sample mean = 40.9
standard error = E = 1.96[10.5/sqrt(120)] = 1.96*0.95851 = 1.8787
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95% CI: 40.9-1.8787 < u < 40.9+1.8787
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Tell me if you do not understand what is happening in this solution.
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Cheers,
Stan H.
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