1) 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 36 bulbs has an average life of 780 hours, calculate the 95% confidence interval for the population mean of all bulbs produced by this firm
2) Is it true that the confidence interval is narrower for 95% confidence than for 90% confidence? Explain
3) Is it true that the Sample means are less variable than individual observations as n→∞ ? Explain
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