II'E'N I: I :- Inn-1 Construct a n 96 condence interval for thedifference between the mean lifetimes of two kinds of light bulbs, given that a random sample of 40 light bulbs of the rst kind lasted on the average 41 hours of continuous use and 50 light bulbs of ' the second kind lasted on the average 40. hours of continuoususe. The population standard deviations are known to be 01-: 26 and a; = 22. Solution For a = 0.06, we nd from Table III that 20.03 = 1.88. Therefore, the : 94% condence interval for #1 #2 is 262 222 ' (413402)-1.ss-1/+E