Twelve dieters lost an average of 11.3 pounds in 6 weeks when given a special diet plus a herbal formula. A control group of twelve other dieters were given the same diet, but without the herbal formula, and lost an average of 9.1 pounds during the same time. The standard deviation of the sample was 2.2 and the standard deviation of the control group was 2.5. Find the confidence interval for the differences of the means.