q9:

The lifetimes in hours of two brands of batteries follow normal distributions with means [1.x , pyrespectively and equal but unknown variances. Independent random samples of 5 batteries from each brand are taken and the following data are observed. Construct a 90% confidence interval for the difference HX [LY . Brand _Sample mean Sample variance O (-7.94,47.94) O (-17.205720) 0 (-16.66,56.66) O (-13.275327)