(a) 95% = mean ± 1.96 SEm
SEm = SD/√n
(b) 90% = mean ± 1.645 SEm
1 = 1.645 SD/√n
A film alliance used a random sample of 50 U.S. citizens to estimate that the typical American spent 78 hours watching videos and DVDs last year. The standard deviation of this sample was 9 hours.
(a)
Develop a 95 percent confidence interval for the population mean number of hours spent watching videos and DVDs last year. (Round your answers to 2 decimal places.)
Confidence interval for the population mean is between and .
(b)
How large a sample should be used to be 90 percent confident the sample mean is within 1.0 hour of the population mean?
1 answer
1 answer