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The mean and standard deviation for the charge time of a random sample of 25 iPhones...

The mean and standard deviation for the charge time of a random sample of 25 iPhones were found to be 23 and 2.5 hours respectively. Assuming that the charge time was normally distributed. A 99% confidence interval for the mean charge time is: Select one: a. 23 +/- 0.77 b. 23 +/- 1.40 c. 23 +/- 1.29 d. 23 +/- 1.25 e. 23 +/- 0.91

Math   Statistics-And-Probability   
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Answer #1

Solution :

Given that,

t /2,df = 2.797

At 99% confidence level of is ,

t/2,df * (s /n)

23 2.797 * (2.5 / 25)

23 1.40

option b. is correct

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