Much discussion has appeared in the medical literature in recent years on the role of diet in the development of heart disease. The serum-cholesterol levels of a group of people who eat a primarily macrobiotic diet are measured. Among 20 of them, aged 20-39, the mean cholesterol was found to be 200 mg/dL with a standard deviation of 50 mg/dL. The mean cholesterol level in the general population in this age group is 230 mg/dL and the distribution is assumed to be normal. A two-sided hypothesis test at a 0.05 significance level will be conducted to test that the group of people on a macrobiotic diet has cholesterol levels different than those of the general population. What is the test statistic value