Question

An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 35 hours. If a sample of 50 bulbs has an average life of 900 hours, find a 98% confidence interval for the population mean of all bulbs produced by this firm.A properly labeled figure of the normal distribution curve and x and/or z values is required for each problem

Answer 1

                                                                                                                                

(1-alpha)*100% confidence interval for population mean=sample mean±z(1-alpha/2)*sd/sqrt(n)

98% confidence interval =900±z(1-0.02/2)*35/sqrt(50)=900±2.33*35/sqrt(50)=900±11.51=(888.49,911.52)

	z-value	margin of error	lower limit	upper limit
98% confidence interval	2.33	11.51	888.49	911.52