The lifetime of light bulbs manufactured by an electrical company is approximately normally distributed with a standard deviation of 50 hours. The average lifetime of a sample of 25 bulbs has been measured as 750 hours. a) What is the 90% confidence interval of average lifetime of lightbulbs manufactured by this company? b) How large of a sample is needed to be 96% confident that the sample mean will be within 12 hours of the actual mean?
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645\) for a 90% confidence level, \(\sigma = 50\), and \(n = 25\). Show more…
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Sri K.
a) An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm. b) How large a sample is needed if we wish to be 96% confident that our sample mean will be within 10 hours of the true mean?
Madhur L.
Lightbulbs of a certain type are advertised as having an average lifetime of 750 h. The price of these bulbs is very favorable, so a potential customer has decided to go ahead with a purchase arrangement unless it can be conclusively demonstrated that the average lifetime is smaller than what is advertised. A random sample of 50 bulbs was selected and the lifetime of each bulb determined. These 50 light bulbs had a sample mean lifetime of 738.44 h with a sample standard deviation of 38.20 h. What conclusion would be appropriate for a significance level of .05$?$
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