1. The quality control manager at a lightbulb factory needs to estimate the mean life of a new type of

1. The quality control manager at a light-bulb factory needs to estimate the mean life of a new type of light-bulb. The population standard deviation is assumed to be 50 hours. A random sample of 30 light-bulbs shows a sample mean life of 475 hours. Construct and explain a 90
% confidence interval estimate of the population mean life of the new light-bulb.
2. A survey of first-time home buyers found
that the sample mean annual income was $46,000. Assume that the survey used a sample of 20 first-time home buyers and that the sample standard deviation was $1,200. Compute and explain a 95
% confidence interval estimate of the population mean.
3. A telephone poll of 750 American adults asked where would you rather go in your spare time?
One response, by 275 adults, was the Mall. Compute and explain a 99
% confidence interval estimate of the proportion of all American adults who would respond the Mall.
4. For problem #1 above, what size sample would be needed to achieve a margin of error of 15 hours or less?

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