business statistics

17.(a) You are working as a purchase manager for a company. The following information has been supplied to you by two manufacturers of electric bulbs: Company A Company B Mean life (in hours) 1,250 1,288 Variance (in hours) 25 36 Sample size 20 24 (i)Test whether there exists a significant difference in the mean life time of these two types company (use a = 0.01). (ii) Obtain 95% confidence limits of the population mean. (b) In a simple random sample of 620 men taken from a big city in which 370 are found to be smokers. In another simple random, sample of 825 men taken from another city in which 420 are found smokers. Do the data indicate that there is a significant difference? in the habit of smoking in the two cities