A special diet is intended to reduce the cholesterol of patients at risk of heart disease. If the diet is effective, the target is to have the average cholesterol of this group be below 200. After six months on the diet, a simple random sample of 50 patients at risk for heart disease had an average cholesterol of 192, with standard deviation s = 21. Assume the distribution of the cholesterol for patients in this group is approximately Normal with mean μ. A statistical test is conducted to determine if there is sufficient evidence that the diet is effective in meeting the target. 

The appropriate degree of freedom for this test is .