In a test of the effectiveness of garlic for lowering cholesterol, 25 patients were treated with raw garlic. The changes in their levels of LDL cholesterol (in mg/dL) had a mean of 0.4 and a standard...

In a test of the effectiveness of garlic for lowering cholesterol, 25 patients were treated with raw garlic. The changes in their levels of LDL cholesterol (in mg/dL) had a mean of 0.4 and a standard deviation of 21.0.

a. Find the 98% confidence interval estimate of the population standard deviation.

b. Does the results indicate whether the treatment is effective? Explain the answer.