A retrospective study of 108 pairs of twins was performed. The twin pairs each had one male child and one female child. Their birth weights were studied to determine if the male twin was consistently heavier. The difference in weights was calculated by subtracting the female weight (in ounces) from the male weight (in ounces): d = Im - Is After looking at 108 pairs of twins, the study finds the 90% confidence interval for the mean difference of weights (in ounces) is: -0.5 A study was conducted to test whether marijuana use impacts your short-term memory. A simple random sample of college students that do NOT use marijuana was taken, and given a memory test in which they were shown items in a particular order then asked to recreate that ordering. A second simple random sample was taken of college students that use marijuana 4 - 7 days per week, and they were given the same memory test. A higher score on the memory test indicates better memory recall. (1 indicates the population mean memory recall score for non-users. 142 indicates the population mean memory recall score for marijuana users. The 9% confidence interval for the difference of means was found to be: 1.9