Question

The lifetime of a certain brand of battery is known to have a standard deviation of 19.8 hours. Suppose that a random sample of 100 such batteries has a mean lifetime of 33.3 hours. Based on this sample, find a 90% confidence interval for the true mean lifetime of all batteries of this brand. Then complete the table below Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place. 0 What is the lower limit of the 90% confidence interval? What is the upper limit of the 90% confidence interval? 5 2

Answer 1

T= 19.8 na 100 X = 33.3 Confidence intervals 0.9 d = 1- 0.9= 0.1 2/22 0.05 6) Population Standard deviation is known so will use Z- table distribution. = +1.645 (using Z-table) Zcritical = Z2/2 20.05 X + Zya 90% confidence ce integrala sta 11 = 33.3 + 1.645 * 1918 vioo = 33.3 + 3.2571 = 33.043, 36'557 The lower limit of the 90% confidence interval=33.0 The upper limit of the 90% Confidence interval=1366