Please help with question! Thanks

Statistics
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Need answer quick please.  thanks

The lifetime of a certain brand of battery is known to have a standard deviation of 19.8 hours. Suppose that a random sample of 70 such batteries has a mean lifetime of 35.8 hours. Based on this sample, find a 90% confidence interval for the true mean lifetime of all batteries of this brand. Then complete the table below.

Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place. 

Jun 21st, 2015

Thank you for the opportunity to help you with your question!

using for confidence interval IC= Z*s/n^0.5; z for 90% is 1.28; you have n= 70 and  s=19.8

so the IC is 3.029 hours, so

 a) the lower limit is 19.8-3.029=16.771 hr

 b) the upper limit is 19.8+3.029=22.829 hr


Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 21st, 2015

Is your answer round to nearest one decimal?

Jun 21st, 2015

 sorry, it is because of time was running out since the system has own time. The rounded off  answers are

a) the lower limit is 19.8-3.029=16.8 hr

 b) the upper limit is 19.8+3.029=22.8 hr

Feel free to ask more questions on statistics. 



Jun 21st, 2015

Thank you!

Jun 21st, 2015

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