Question: A group of 250 similar tree is divided into subgroups a and b consisting of 120 and 130 trees respectively for purposes of testing a new fertilizer. Group “a” receives the new fertilizer while group “b” receives the old during the study. During the study the mean number of inches of growth for group a is 4.5 with a sd of 0.59 inches the mean number of inches of growth for group b is 3.26 with a sd of 0.89 inches .Find the 90% confidence limits for the difference in the mean number of inches of growth for the two groups